The term "fantasy sleeper" is rather stupid at this point.
There is so much written, so many forums and so much media, no one is a sleeper.
You think Gio Gonzalez is a sleeper this season? He's not. Everyone knows who he is. They might not like him as much as you do, meaning you will be able to draft him late, but he is not being slept on.
The new term should be "fantasy value" as in: so-and-so has great fantasy value because of how late he is being drafted. So, hypothetically, what's the best lineup that can be put together of players who no one wants, all undrafted players? This would show us ultimate value, adding a player off waivers who can produce all year.
Here is 2011's Best Fantasy Baseball Team No Money Can Buy.