Computers opponents are a great addition to chess, mostly liked because they're always on hand.  But there are more to computers then that, from special features like customizable personalities and openings, to more basic features like takebacks and pausing, I want to know some programs people use!

I prefer to use chessmaster 11 on my own PC. While its features are fun, what I love about the engine is that its weaker opponents have relatively accurate positional and tactical weaknesses.  It isn't like other engines where it will kill me if a tactic is 6 plys ahead but will falter if one is 7 ply.

On the internet, I like to use GNU chess (http://chess.delorie.com/), I find it one of the toughest internet opponents to beat!

Chessmaster 11k GM Edition.  I set it up at my table with my board and play it OTB.  It's great because I can set a level or style that I want to play against and as you say MBickley, it fairly accurately reduces it's strength accordinly.

I use Rybka and I plan on buying Deep Junior in the future.

i sometimes play chessmaster on a nokia cell phone