Every year players start out as sleepers, but by April they have nowhere to go but down. There have been names that are already getting so much hype this year that we can see by the time you draft they will be less of a sleeper.
Nelson Cruz - OF - Texas Rangers
I have written how much I like Cruz. He is a potential five-category player, with average being his one weakness. He has already been picked as the opening day cleanup hitter, and he also has surprising speed for someone known more for his power potential. He has now been covered by plenty of sites: Roto Authority, Fangraphs and RotoProfessor.
This is the type of player who is currently going in round 16, but by opening day will be 3-4 rounds earlier with all the hype, and he will no longer be a great value. In the case of Nelson Cruz, a selection in the 16th or later rounds would be a great pick, but don't set your sights on him so much that you feel the need to pick him anywhere above the 13th round.
Other Sleepers becoming overhyped: Matt Wieters, Pablo Sandoval and Brandon Morrow (as a starter or closer)