How can I add more rounds to AES? I'd like to understand a bit more about the AES key schedule if anyone would mind explaining that. For instance, why is the way the schedule generated (with recursive xors and occasional substitutions) more secure than say, using pbkdf2 on the key, then using it on the result, and on until there is enough data?

The reason I ask is because I'd like to experiment with an extended AES implementations, with more rounds, but need to devise a way to generate the extra sub keys.
The AES key schedule isn't more secure than using PBKDF2 on the data -- but it is a lot faster, and requires many fewer gates in silicon.  Performance is important.

As far as devising your own variant of AES, with more rounds: don't do that.  There's no good reason to do that (it is exceptionally unlikely that AES is the weakest link in your system), and you can easily introduce subtle security vulnerabilities.  Whatever problem you have that you think motivates this, modifying AES isn't the solution.