The staff over at FakeTeams, SB Nation's site for all things fantasy-oriented, has published a six-part series discussing unheralded prospects, per MLB division. Sleepers and unheralded prospects are a key focus at Minor League Ball, so I wanted to give the FakeTeams guys props for their work here.
American League East Unheralded Prospects, by Jack Cecil
American League Central Unheralded Prospects, by Michael Schwarz
American League West Unheralded Prospects, by Jason Hunt
National League East Unheralded Prospects, by Domenic Lanza
National League Central Unheralded Prospects, by Michael Schwarz
National League West Unheralded Prospects, by Ray Guilfoyle
Some of my favorite names show up on these lists, including Josh Hader, Clayton Blackburn, Silvino Bracho, and Tony Kemp. Some of the guys on the FakeTeams lists do rank highly on some prospect lists but I do think it fair to say that guys like Hader and Blackburn are often under-rated or under-mentioned by mainstream sources.
In any event, the series is worth your time to read and study.