Well, it depends which GameShark version you have. If you have Pro ActionReplay (a better version of GameShark IMO, made by Datel) then I'd reccomend GameFAQs.com
MadCatz bought the rights to the newer versions of GameShark you mau have seen on the shelves such as the GS for the GBASP (which is much more limited code-wise compared to Datel's GS); if you have one of these, you may need to wait a while, since the Official Site
doesn't have anything for them yet. Nor do many fan-made webpages at the moment, which means that the games are new and probably still being hacked.
If I ever run into anything though, I'll let you know.