Marco Sowa created a new archive site which tries to be an index for all released Amstrad CPC games and tools, containing screenshots, covers and ratings. The website is a community driven project, so you can help with voting for your favourite games and help with sending screenshots and cover images to improve the content. Visit http://www.cpc-history.com and help by contributing to the database.
You are searching for a game where you only can remember a part of the gameplay or some screens? Then you can use the Amstrad CPC Screenshot Catalog, which was assembled by Lex Sparrow and ZX4Ever, to find the game. It currently contains more than 3500 screenshots (only in-game screens – v1.0 contained loading screens, too).
You can download the PDF file from PressPlayThenAnyKey or the CPCWiki share hosting.