I've never kept Angelfish so all I know is that they need a fairly deep tank and will eat just about anything they can get their mouth around (no neon tetras with them, for certain). Angels get to about 6in long (and taller than that) so you won't have too much room to keep other fish after that. Angels CAN live in smaller conditions, but they will be stunted; part of that whole "Survive vs. Thrive" thing. Otherwise:
Guppies/Platys/Swordtails: All livebearing fish and fairly easy to stock and take care of. Pretty hardy and tolerant of water conditions. They don't need to shoal. As long as you keep the ratio of males to females at 1m:2+f they should all get along great. They WILL produce fry (perhaps even if you have no males, since they can save genetic material for later) so you'll need to have a plan for getting rid of them. (your LFS will probably take them, just ask.) I'm not sure but I think if you have all male guppies they do get along, but again ask someone who's kept them. If you DO want to breed livebearers, be warned that platys and Swordtails can interbreed (Plordtails?). Fancy guppies (the ones with the huge colorful tails) are slow swimmers and may get their fins nipped, so make sure you avoid tankmates with a fin-nipping reputation if you get them. If you try livebearers with angels, the adults should get along fine, but the fry will be consumed.
Gold Barbs: A few warnings, but nothing too tough. They'll need to be in a shoal, and they're "subtropical" which means you'll want to keep the heater lower than the standard 78F. They're fairly tolerant of water conditions, but prefer acidic. Because they need to be in a shoal of at least 5, they'll take up a fair chunk of space. Otherwise my quick google search (again, i have not kept these) says they're peaceful and easy to take care of.
Neon Tetras: These have a history of being more difficult to keep than advertised. They aren't very tolerant of hard or basic water, and also do not acclimate quickly to changes in water condition. Captive bred fish tend to do better in this regard, but some neon breeders are not very responsible, so the quality of fish available varies quite a bit. They will need to shoal, but at least they are smaller than the barb. Angelfish are natural predators of Neon Tetras, so clearly that is not a good idea. There is even a "Neon Tetra disease" which is uncurable, so a quarantine tank (and avoid live food) would be a very good idea if you want to keep them. I don't mean to tell you to never buy Neon Tetras, but just to warn you that they aren't really the best beginner fish.