I've mined with a few ASICs before, which was nice and easy.  I find GPU mining a bit more difficult, for lack of coins and software.  For instance I can't modify an old Bitcoin release and use an old Bitcoin GPU miner to experiment with (or any coin that uses same proof of work).

GPUs should be quite flexible (still) if not profitable.  I'm fascinated with the subject and would like to learn a bit more, so after changing the proof of work in some version of Bitcoin, I could try and verify it with GPU mining software.

Maybe if there's a good keccak/something else GPU miner, I could rip out SHA256d and try that out.  Not sure what GPU mining software is flexible enough to handle a lot of algorithms though. Can anyone recommend a good GPU miner?

Thanks