I'll answer half of your question to the best of my ability. I'm in a re-build myself and these are guys that I would look to hang onto:
Up front:

J.Audy-Marchessault - CBJ--shows promise
B.Bennett - Pit-Even just trade value should make him worthy of hanging onto(play with Malkin/Crosby?)
M.Frk - Det (has talent, but I'm not super high on him. I may consider moving him to take a shot)
J.Gaudreau - CGY(I don't know a ton about him, but others seem to be high on him)
K.Kabanov - NYI( I stil feel he has top six upside --eventually)
A.Killorn - TB (a chance at cracking the TB roster?)
M.Nieto - SJS (Don't know a ton about him either, but from what I've heard, he has speed to burn)

Back End:

N.Beaulieu - Mtl (Should be a good pt guy, I'd think a nice tandem with PK)
J.Morrow - Pit (Again I think trade value alone makes him a no-brainer. Should be a solid player with good upside)
A.Petrovic - Fla (Some feel he has PP QB written all over him, and he's putting up some PIM's as well.)


I hope this helps..although I'm definitely not the most knowledgeable on thses guys.