Instructions
Use the official GameShark website. The GameShark website provides regularly-updated codes for a variety of consoles including the PlayStation 2, Xbox and Gamecube. Select "Codes" from the column on the left side of the screen and click the icon for the console you are playing your game on. Find the name of your game and click on it to view a list of available codes.
Use GameFAQs.com. GameFAQs is a site that provides walkthroughs, regular cheat codes and GameShark codes for almost all of the games ever made. Search for the game you are playing by name using the "Search" feature at the top of the page. Click the title of the game in the "Search" results and select "Codes" to view a list of available GameShark codes for that title.
Search for your game on Neoseeker. Neoseeker is a site similar to GameFAQs in that it provides guides and walkthroughs for games in addition to codes. Browse through a list of games by console or search for the name of your game directly from the main site. Click on the "Codes" link in the page for the game you're playing to view a list of all available GameShark codes for that title.