I got Shredder a while ago but its expensive. Most chess studying I now do on the computer is with free database software called SCID (http://scid.sourceforge.net/) loaded with a free database (http://www.top-5000.nl/pgn.htm) with a free engine (Stockfish) loaded on it. I downloaded it after checking out a good video tutorial on SCID, available here: http://www.chessvideos.tv/forum/viewtopic.php?t=6461
Hope that helps!
I like Sigma Chess. It's free, easy to use, and does pretty much anything I'd want a chess program to do. The website explains all the features: http://www.sigmachess.com/