Guppies are tropicals. You want to stay in that category. Like mollies, danios, and catfish (most). <--- just to name a few! You could put one betta in there. Bettas are fighting fish and do not tolerate other Bettas but could possibly get along with your guppies. Some Bettas are very aggressive and will mistake the guppies beautiful fins for a Betta. Good luck :)
Guppies can be put together with mollies, betas and platys. They are actually considered good community fish for getting along well with other types of fish. Check http://www.petinfo4u.com/guppies.htm for more details.