Like I mentioned in my first post, livebearers can be great community fish, or bad community fish.
For the most part, guppies, platies, and (This, I believe, though I admit I'm not well versed with) endlers are good community fish. Also, as I said before, guppies are one of those fish that can get picked on by the wrong tankmates, but the others are usually pretty good.
Swords can be great, at their somewhat bigger size, but can be territorial with the wrong tankmates, and sometimes be nippy. It's just in their nature.
And again, mollies can have environmental issues, so it's best to consider what else is in the tank before considering adding them.
All that said, however, these fish usually behave quite well with eachother. I might suggest keeping platies and swords sperate since they can, and will breed, and it could also cause heightened aggrivation between any males.
I'd also go with what Annistasia said (We have similar tastes, apparently

), having either platies, guppies, or swords (8, 8, or 6 respectively) in with a school of tetras (Go by habitat for this decision) and some corries on the bottom. It gets good interactivity, and action on all levels of the tank.
Of course, all this is still assuming a totally empty 30 gallon and not additional stocking.