I've had many different kinds of freshwater species over the years. I'll share my thoughts about them.
Guppies: I've had lots of guppies. They are extremely hardy fish and are one of the more long lived ones I've seen. They come in many attractive colors, including rainbow varieties, and are very low-maintenance. Highly recommended fish!
Platys: I was never a fan of these fish... :/ Mine were always shy and never swam around much.
Also, they always seemed to get the most food out of all the fish. They always got nearly all the bloodworms when I tossed in a cube as a treat. Don't like them much.
Mollies: These are OK fish. They don't live a terribly long time in my experience, but they are an attractive, hardy addition to a community tank.
Swordtails: I love the way these guys look, but they're frail and bully-ish. Not my favorite fish, but they look really cool!
Some other good beginner Freshwater Fish:
Neon Tetras: They are fragile, very, very fragile, but they're gorgeous, don't bother the other fish, and live a long time.
Red Miner Tetras: These things live forever. They aren't very exciting, but they mind thier own business, are happy to feed on the food that falls in the middle, and as I said, live an incredibly long time.
(There are many more tetra species, and I've tried a lot of them, just can't think of any atm.)
Danios: A personal favorite! Sure they aren't very colorful, but they're nice, long-lived, and very amusing. They love swimming through things and are also intelligent. Mine approach the glass as if saying hello whenever I get close to the tank.
BOTTOMFEEDERS:
Upside-down catfish:EXTREMELY long-lived. My first one, who was in my initial group of fish, is still around today! (He's four years old.) They're nocturnal and will sleep in a ceramic cave or other hiding place if you give them one. And yes, they really do swim upside-down!
Sucker fish: Probably my favorite fish of all time. They get HUGE, live long, are hilarious-looking, and will just eat the algae off the glass. (I also give mine algae wafers.) A very awesome fish that I highly recommend!
I hope this helped!
Also, if it interests anyone, currently my tank contains: A suckerfish, an upside-down catfish, red miner tetras, neon tetras, danios, and guppies.