I don't know if I can come up with 12 but I will throw a few names out there for discussion. Perhaps a little biased to players I have played with in my days.
Rob Merkl - probably the best goalie to play in the Valley.
Dave Woodsford (sp?) - Incredible talent.
Martin Vido - Best Defender I played with. Not a lot of flair but very solid.
Joe Demchak - Slovan sniper with questionable heart. Only a few years in premier but scored at will when he felt like it.
Cam Willmets - not the happiest guy - but the best in todays Valley.
Pete Hjorth - Because he is on every other list!
Murray Howes - May be off on this one. I hated to play against him.
Arnie Meers - Don't think he played many years in the Valley - effective when he did.
Paul Marshall - love him or hate him - you always knew he was there.
Perhaps someone can add to the list. Hard to come up with 12. I am sure I missed a few obvious ones.