http://bluesguitarunleashed.com – this is just a fun little lesson I put together for my songwriter students. It’s actually really easy to figure out which chords can go together and make a song out of them.
Obviously this isn’t all you need to write a hit song, but it’ll at least give you a system for coming up with some chords you like.
There’s another cool side benefit, if you get used to thinking about chords this way, you’ll often come up with something you recognize from another song. When you do that you’ll know what the chords are in that other song and you’ll recognize that progression in other songs… it’s cool.
Have fun with it!