i dont have any experience with a heated tank, but if you want hardy fish a goldfish is your best bet. if you're starting from scratch maybe get some comets. they are like 18 cents here. that way if something goes wrong with your cycle or what not then you dont lose too much money. you might want to let to go for a day or two on its own. no fish. put some fish food in there. pretend there are fish that will help you with your cycle. if you can get your hands on some "Cycle" [thats what my bottle says] and follow the directions that would help you too. there is also another one that Byron uses that is good as well. He has uses Cycle as have I and my tanks are fine and dandy. as for some good fish try Golden dojo loaches if you can find them at your lfs. they are long eel like fish with sort of sucker mouths. more like a carp rather than a pleco.
these are very unique fish. they secret a mucous so if they get out of your tank they can live for THREE days. so if it were to get out and you see it all dry and icky you could put it back into the tank and it would probably make a full recovery. also if you touch them while they are in the tank they feel slimey where another fish would feel "normal"
they also store oxygen in their intestines so they can "breathe" outside of the water. its cute to see when they take too much air in. their bums start to float up and they will eventually "fart" to get rid of the extra air.
they even become "friendly" with their owners. they'll get used to seeing you walk around. they will even learn their feeding time. mine will see me walk and their heads perk up. if they see, hear, i unno how they know but once the lid opens they shoot out in search for their flakes. if you have your hand int he tank to move stuff or clean it they will nuzzle your hand like a cat and even kiss your hand. mine have even eaten out of my palm. my one female in my 20 gallon will sit in my hand if i curl my fingers in a hook. i love he muchly
other than that id say a goldfish. they are kind of boring and poop a lot. i dont think they are good with many other fish because they do eat a lot and they eat fast so fish like Betta that like to take their time and eat dont make good tank mates. most betta are pretty aggressive too.
Guppies would probably work. they are also known as the "million fish" because they reproduce like rabbits. you could get a male and two females and just wait for the females to have babies, and get more fish. if you dont use a net or some sort of separation or have cover for the fry the adults may eat them though. they are pretty good at surviving as starter fish though. im pretty sure a sword tail is basically in the same boat as the guppy. im not too sure though.
a nice plecostomus [pleco] would be a nice addition once you feel your water levels are safe to sustain fish. a pleco will help to keep your algae levels at bay and itll keep your glass/plants/decorations squeaky clean! they are fun to watch clean too. they live quite a bit and get kinda big too. i think 5" or so. one would be enough for your tank, or snails. problem with snails are that if oyu get dojo dojo will eat your snails if they are not fell enough.
i hope that helped! im kind of all over the place. im no good at orginizing my thoughts! i do recommend the dojo loach though. they are really hardy fish. they live 2-6 years. they get about 6"-12" [i think 12"] long, and they go crazy for bloodworms. also they are sensitive to barometric pressure! so they get really active the night before a storm!
here i go rambling again >.<
sorry i love my little dojos
anyway! welcome to the forum.
welcome to the hobby! if you need anymore help im here and so are the many other folks!
good luck bro!
EDIT:
i like your avatar
L from Death Note XD nice choice