Jason Hunt and I published our 2012 fantasy prospect rankings by position awhile back, but here are links to the rankings:
Catcher
First Base
Second Base
Third Base
Shortstop
Outfielder
Starting Pitching
Relief Pitching
Bret Sayre published his Top 100 Dynasty League Prospects for 2012:
Prospects 100-51
Prospects 50-1
Craig Goldstein published his Top 12 Fantasy Hitting and Pitching Prospects for 2012:
Top 12 Fantasy Hitting Prospect for 2012
Top 12 Fantasy Pitching Prospects for 2012