I have an old Gameshark

[xibalba]

.

[Mezmorize]

I would recommend checking out this site:
http://psone.psx-scene.com/museum.htm

[BigBossman]

I used to have a Gameshark Pro. That thing was awesome. You could hack your own games with very little trouble. You should be able to find one easily on Ebay or Amazon.com. I wish they made that device for every system. When the PS2 came out, they totally did away with it. Now on the PS3 & XBox 360, you can't even hack a game without modding your system.

[Mezmorize]

I've bought more than one brand new PS1 GSPro's from:
http://stores.ebay.com/Video-Games-Source