Well, it depends on what you mean by sleeper. With sites like this giving so much information, it's hard to find an unknown player. The word "sleeper" is evolving into meaning "value pick." That's fine with me.
Under that definition, Vernon Wells probably is a sleeper. He probably isn't as good as he was in 2003 but not as bad as he was in 2004. So he'll go later than what his production will warrent. Other guys like that are Pedro Martinez, Richard Hidalgo, G. Mota, and Shawn Green. Derek Lowe is in for a big, big season.
As for younger guys just getting established, how about David Wright? Jeremy Reed? Clint Barmes? Jose Capellan? Jeremy Affeldt?