Tetra's are fine with guppys, and other livebearers, corys,plecs, no gouramis or betta fin nip the guppys tails, danio are fine, no barbs to aggressive and fin nippers.
Not all Tetras work, as some can be nippy. Also, depending on the Danio, they can be nippy too. And, not all Barbs are aggressive, some are very peaceful, like Cherry Barbs.
But yes, as Wilder said, most other common Livebearers will be fine, Cories and Plecos are good, Rasboras are always nice.
What kind of fish do you want? Like schooling fish, or a few "centerpiece" fish, or what?
It depends wether you want your centre fish to be a bottom dweller or mid to high level dweller.
A peaceful bottom dwelling fish for example would be a bristnose plec, even a small group of them, here is a link with more info a pics on them;
for other peaceful community bottom dwelling fish corys make a good choice but do best in groupd of 4+, albino, bronze and peppered corys are very hardy ones in particular;
These are just some ideas for your tank stocking, always research your fish yourself as much as posible before you get it, if you tank is new i also strongly suggest you read up on "new tank syndrome" in the pinned articles at the top of the beginners section .
I have one cherry barb left and he chased my corys so had to move him, he's a little charactor, but he settled down now, joined my glow light tetra's who he used to chase about.