Hi Matthew, welcome tothe forums.


Iuse Rosco gels on my 580 exII and 420 exII. You can buy a strobist kit for around $15 that has plenty of different colours including the standard CTO's etc.


In terms of attaching to the flash there's a few options. I made a gel holder out of a piece of acrylic bent over onto itself and with a 90 deg bend in it which I velcro to the flash unit. Works just fine.


Cheers, Ben.