There aren't many games that can be "hacked" comparative to the entire PS3 collection (PSN and disc based).
This site does however, list the games that DO work, and there are forum members that are constantly looking for new tricks to do. They just need the game saves.
That's mostly just for trophy hacking though. For anything outside of Trophy related issues, there are sub forums focusing on specific games, maybe try looking there.
Lastly, the majority of this "hacking" stuff, is just using a hex editor on a save file, and seeing if we can manipulate the data on there to suit our needs.
This site isn't here to teach you how to use a hex editor, as there are more than enough sites out there to do that. We just show you what can be done, if there is a game that can be edited in some way.
I hope this helped answer your question.