Without checking I would say CardArtManalink folder is supposed the biggest.
If you don't play Shandalar you can always remove/backup CardArtShandalar but it's a measly 33 Mo folder for me while CAM is around 320 Mo
If you have PDA installed in your Magic root folder logs files can raise quickly if you use it often, I am already at 150 Mo of logs but it's because I convert a lot of NetDeck and do a lot of deck check (and I need to keep the logs to track the decks history).
If you have some mods installed, maybe look for additional land or avatar images but I don't think they "weight" much
Anyway, best way to check HD space issue is to use the great and free
HDgraph, software that precisely calculate what contains your HD or folder in a nice colored graph
The Ciroth clean version available on 4shared is 320 Mo and the Card image free is only 90 Mo so maybe you can compare with your own folder.