Shredder claimed to have human-like play at lower levels, so I gave that a try. It works surprisingly well at my level, making plausible mistakes in a fairly consistent manner. When I was playing against it I was in the 1200-1500 range, so I don't know how well it does at higher levels. Also, it had a setting where it would rate you and auto-adjust itself for the next game.

It made playing against a program a lot nicer than other chess programs I had tried.