Copy/paste of the GBC one, lulz.

Gameshark
This has mixed GB/C codes.
http://gshi.org/?s=v2&sys=10 also has some pretty good codes.

If you know of any other good sites, post 'em here.

i tend to search gamefaq for localised cheat lists.

VBA-M | NGOHQ | Post Impact Productions | TNHW | XBCD 0.2.7

The old GSCentral which recently got ruined was pretty good for them. Some awesome people moved it over to BSFree like it used to be in the good old days though. http://www.bsfree.org/
There's also ANTI-GSC which is pretty much the same thing but has a different look.

Lol, the first link I posted was to BSFree. No harm done.
The community moved over to Kodewerx.

Anti-GSC is also outdated, btw. It had a copy of GSC's database from several years back.

Do'h I only saw the the second link.....sorry about that....links should be in a more discernable colour I guess...