What else is in the tank? Is it cycled?
Kissing gouramies grow large and will often dessimate plants so might not be the ideal choice for you. They are also capeable of eating very small fish and are territorial. Their name comes from the mouth-locking they engage in when fighting (other gouramies do this also). They can get to 10" easily, sometimes to a foot long. They are impossible to sex until they spawn so you'd be better off with just one.
Dwarfs I would not reccomend. They are very prone to disease so you should only consider them if you are familiar with a local breeder. Don't buy from an LFS. These you can keep in groups with two or more females per male, allowing about 10 gallons per male, 5 per female. Females are not as colorful as males and can, therefore, be harder to find as LFSs don't stock them. Obviously, you wouldn't have this problem with a breeder anyway. As they stay small and won't bother other non-gourami fish, you can fit several in your tank.
Three-spots come in several color morphs including blue, gold, platinum, lavender, opaline and cosby. They grow to 5-6" (males being larger than females) and are one of the most aggressive species around. If you'd be happy with only one, a male would be fine. Otherwise, a group of 4 or more females and no males is the best option. You have to watch what you keep with them - guppies, easily stressed fish and top-dwelling or territorial fish are at risk. Anything that nips might also be nipped back. Sexing these, thankfully, is easy as males have notably longer and more pointed dorsal fins. If you happen to make a mistake and end up with a spawning male, you may well suffer many non-gourami casualties (which is unusual amongst the majority of gourami species which tend to pose a greater threat to their own kind). The good news is that these are immensely hardy and that you can mix the colors as you like.
The above species are not safe to mix.
Alternatives now...
Instead of dwarf gouramies, consider thick-lipped or banded gouramies (Colisa labiosa and Colisa fasciata respectively). The former grow to 3.5" and the latter to 4". They are both peaceful and colorful species (even the females) that look quite similar to dwarfs and have pretty much the same requirements though their larger size means you need to watch you'r enot over-crowding. The banded is a particularly active and out-going species as well.
Take a look at these pictures:
Banded:
http
/www.aqua-fish.net/imgs/fish/colisa-fasciata.jpg (female below)
http
/www.tjorvar.is/assets/images/autogen/a_fasciata.jpg
http
/www.akvariesiden.dk/fisk/billeder/l..._1363299715.jpg
http
/www.fishbase.org/images/thumbnails/...tn_Cofas_u4.jpg
Thick-lipped:
http
/aquaworld.netfirms.com/Labyrinthfis...sa_labiosa1.jpg
http
/www.aquanet.de/objimages/2003092717...31751083161.jpg
http
/www.ryedaleaquaristsociety.co.uk/Q%20PIC%201.jpg
As you can see, C. labiosa comes in a handfull of color morphs that you can mix.
You can mix. these species but aim for the 2:1 ratio of females to males within each species and make sure they have room. (so maybe a trio of each but not more)
The other alternative is the pearl gourami - Trichogaster leeri - my personal favourite. These are stunning and sociable, peaceful fish that grow to about 4-5". A group would be wonderful. You can mix. these with either of the previous two as well but they are far more rewarding if you only keep one species. I'd suggest maybe 2 males and 5 females.
Take a look:
http
/gallery.pethobbyist.com/data/22550gourami.jpg
http
/www.thekrib.com/Plants/People/hurley-pearl.jpg
http
/www.aqua-fish.net/imgs/fish/027.jpg
http
/www.cricalix.net/~dhill/gourami.jpg
http
/www.tjorvar.is/assets/images/Pearl.jpg
http
/badmanstropicalfish.com/sbs/anabantids/sbs_pearl.jpg - pair, female above
http
/www.aquaworldnet.com/awmag/images/leeri.jpg - pair, female below
It's probably obvious but all the first photos are of males. They have the long fin ray extensions and red-orange ventral coloration. They color up more if they are with females so keeping them singly isn't an option I'd consider.
With the three species I've suggested, most peaceful community fish like platies, swordtails and other peaceful livebearers (not mollies) are great - either keep trios or stick to female-only or male-only (not male-only with sowords though, they fight) groups. Non-nippy tetras, rasboras and barbs (eg: rummynose tetras, black phantoms, harlequin rasboras, checker barbs etc) are fine in schools of at least 6. Cherry barbs work well in trios as well. Cory cats, peaceful loaches like kuhlies, dwarf chained loaches, small plecs (eg: bristlenose) and peaceful synos like upside-down catfish make good tankmates too. Avoid top-dwellers like danios unless you're going to limmit the number of gouramies to say 3 (danios are great and not nippy but they compete for space in the upper levels and can cause gouramies stress if they feel crowded). Peaceful dwarf cichlids like rams are also fine (in pairs) with these gouramies (in your size tank) but watch you're not over-crowding the cichlids as they are territorial. Keyhole cichlids are also wonderful in groups with gouramies - their character actually reminds me of pearls somewhat. More unusual tankmates would be a trio of American-flag fish or a shoal of praecox or threadfin rainbowfish. There are many other possibilities as well - anything in particular you had in mind?