Of those gouramies that have been mentioned, the maximum number you should add to your tank is 3. Even that is pushing it because most 29 gallons have the same footprint as a 20 gallon. If you were to combine top-dwelling species with mid-dwelling species, however, you could keep quite a few more.
You have many options. What other fish will you be putting in with them? That'll help narrow things down. Also, if this is going to be an all-gourami tank, it's possible to include some of the species that spend more time in the middle area of the tank (croaking, sparkling, spiketailed paradisefish etc) so you can keep more gouramies in total.
The most common gouramies are:
Dwarf gourami (colisa lalia). The males are more often available because they are the ones with the color so therefore sell much better than females. They are peaceful towards other fish but males are often territorial towards each other and sometimes towards similar-looking gouramies (like those also in the genus colisa). They come in a multitude of color morphs and grow to about 2". The downside to these is that they can easily succumb to stress-related illness and are prone to itnernal bacterial infections (mainly due to mass-production and in-breeding). They are not a hardy fish and not a fish to start your tank with. Like other top-dwelling gouramies, they appreciate floating plants for cover. A single male would work. Alternatively, a trio (1 male, 2 females) would be a good option for a 29 gallon. 2-3 males should also work.
Honey gourami (colisa chuna/sota). These are often confused with the dwarf gourami but grow to a slightly smaller size 9approx. 1.5") and are hardier. They also come in quite a few color morphs but not to the extent that dwarfs do. The young fish you'll see at your LFS are likely to be dull creamy-brown, often with a faint horizontal stripe runnign along the lateral line. They soon color up. Males develop a dark blue-black underside and are over-all more brightly colored. These are peaceful towards other fish, but like the dwarf, males are territorial towards each other. I would reccomend keeping these as a trio (1 male, 2 females) and not with very large or aggressive gouramies. They also appreciate floating plants.
Banded gourami (colisa fasciata). Also known as the 'Indian', 'Striped' or 'Giant' gourami, these are 4" fish with a similar temperament and appearance to the dwarf. Their larger size means that keeping several males is less adviseable but they are also better candidates for keeping a single male with some of the larger trichogaster species which would otherwise bully a dwarf. The name 'Giant' comes from them being the largest of their genus. Don't confuse them with the true giant osphronemus gouramies which get to 30"! These are also quite hardy and would appreciate floating plants. Females lack the very bright banded pattern of the males.
Thick-lipped gourami (colisa labiosa). These get to about 3.5" and are also somewhat like the dwarf and banded in temperament. They aren't quite as attractive, IMO, as the banded or dwarf but they make up for it in character and hardiness. Again, they preffer to have floating plants for cover. Females are duller than males.
Pearl gourami (trichogaster leeri). These are my favourite gouramies - indeed, they are my favourite fish. Besides their very amiable temperament, these are by far the most beautiful and striking fish once mature. The males, in particular, develop a bright orange-read throat and long, trailing fins. These gouramies grow to about 5" and enjoy the company of their own kind. They are often seen 'schooling' if kept as a large group. They are also quite hardy but are prone to being nipped if kept with nippy fish like tiger barbs because of their wonderful fin extensions. They also like to have floating and tall-growing plants for cover. Idealy, a trio would be best for your tank with no other top-dwellers. However, as they are quite peaceful, something small like the honey gouramies mentioned above would be ok to put with them. They will be shy if not kept in a tank where they feel safe but are otherwise a very rewarding fish to own.
Three-spot gourami (trichogaster trichopterus). This is the largest of the commonly available gouramies that you could keep in a 29 gallon comfortably. They get to 6" and come in a wide range of colors, from the wild-type 'blue' to the beautiful 'opaline', striking 'gold', 'lavender' and a near-white 'platinum'. Though they are an extremely hardy and interesting fish, and also the easiest of the gouramies to breed, the males, especialy, are very territorial and both sexes can be terrible bullies and rather aggressive. Because of this, only one male should be kept per tank and, IMO, you shouldn't keep them with any other gouramies unless you have something of at least 55 gallons. Females are calmer and would be ok with the larger species but avoid anything very small or delicate that might get bullied. Non-gourami fish are usualy fine with them. They are out-going and not particularly shy but would still appreciate a planted tank. Males have a more pointed dorsal and longer un-paired fins. Despite the aggression, this is the best gourami to start with if you aren't feeling too confident.
All the above are the more typical, top-dwelling gouramies you will see. Of those, I would keep a maximum of three in your tank. there are a few exceptions but it's safer to stick with that and not risk their lives. They all appreciate a planted tank with, in particular, floating cover. None of them are picky eaters and they don't have any specific requirements except good water quality (like any other fish).
Here are some of the commonly seen mid-dwelling gouramies (and related species) you may come accross. Some are more suitable than others:
Paradise fish (macropodus opercularis). though these only grow to about 3", the males, especialy, if placed together in a limmited space are likely to behave like bettas and fight to the death or severly injure each other. The immature fish at your LFS won't have such tendencies but keep this in mind if you decide to get any. They are best kept singly or as one male with 2-4 females. Males have longer fins and brighter colors. They come in a variety of color morphs and there's also a 'black paradisefish' which is identical in shape and temperament but is often considered a different species (often macropodus concolor though there is debate as to whether that is the real name or not - apparently there are actualy 2 species of 'black paradisefish' and neither is concolor - which may not even exist). Regardless of color, these fish are usualy best left for larger tanks or semi-aggressive tanks. They often become bullies (the males in particular) and may even kill small tankmates. They are best not kept with other gouramies and a planted tank with many hiding places is reccomended. I'd like to emphasise that this stereotypical view of m. opercularis does not apply to all individuals. Some are very peaceful but it's a risk I would not take if you want other gouramies or small, slow-moving fish. An exceptionaly hardy fish that can tolerate low temperatures, historicaly, it was one of the first aquarium fish brought to Europe.
Sparkling gourami (trichopsis pumilus). Barely growing to 1.5", these are a small, peaceful species. Though they alck a lot of the color of the larger species, they are still delicately beautiful with the males, especialy, developing a beautiful series of purple-blue spots along their body and both sexes having a faint blue-ish tint to the eyes. They can 'croak' - usualy during breeding time and when males are competing - and do actualy 'sparkle'. They aren't a sensitive fish but, because of their minute size, should not be kept with anything overly aggressive. I would either keep them as a tiro or in a group of approx. 5-7 (say 2-3 males, 3-5 females) in a heavily planted tank. You can keep some of these in addition to one of the more peaceful top-dwelling gouramies (such as pearl or one of the colisa species) as they occupy the lower levels more.
Croaking gourami (trichopsis vittatus). At first glance almost identical to the sparkler, these little beauties grow to about 2" to 2.5" max. Though they lack the bright colors of other species, they have bold horizontal stripes and striking bright blue eyes. They are named 'croakers' because, like the sparkling gouramies, they have the ability to produce a croaking sound which is often heard when breeding and is made by the males. Also like the sparkler, they are not particularly delicate but can be shy if kept with aggressive tankmates or in a tank with inadequate cover. They could also be kept in addition to a few gouramies from the top-dwelling list in a group of 3-5 with females out-numbering males. They can also be mixed with sparklers as long as you are careful to not over-crowd or over-stock.
Well that's it. There's also licorice gouramies, chocolate gouramies, spiketailed paradisefish, kissing gouramies, moonlight gouramies, snakeskin gouramies and a few others (including the related ctenopomas and microctenopomas) that you may come across but they are, for one reason or another, not suited to a community tank or to your tank's size. Except the spiketails which would be suitable as a trio with more peaceful fish but you are unlikely to find them. Oh, also, don't keep gouramies with bettas as they are related closely and tend to fight.
edit: for my terrible punctuation
Good luck with your new tank! I hope to see pictures soon 
