You can find competitive movesets and natures and everything
here. It's not completely finished (and not every Pokemon is covered) but it highlights the most useful Pokemon in the game today. Also, another good resource is Smogon's list
here: scroll down to about halfway through the OP and there'll be a bunch of spoilers with Gen I, Gen II etc. You can click on those and then the links in there are analyses of Pokemon and their good movesets. If something isn't listed there, then it's really not very good and you probably shouldn't use it on your team if you want to win in the OU metagame. ;o;
Good luck with building your team! :3