Not in any particular order, my favorite folder designs have come from:
Brad Southard (Downing Drop point/Hawkbill, Tozer, Daws, Tarsus)
Brian Fellhoelter (Fotuki)
Peter Rassenti (Ti Integral flipper)
Spyderco (Military), /Sal & Eric Glesser (Paramilitary 2, Calypso), /Gayle Bradley (Air), /Bob Lum (Ti Lum Chinese), /Fred Perrin (PPT)
Farid Mehr (K2)
Ken Onion (Leek, Offset)
Tim Galyean (Lahar, Junkyard Dawg)
Gareth Bull (Warlock, Warlock II)
Kershaw (Speedform, Barrage/Salvo)
Zero Tolerance/Ken Onion (ZT0200), /Rick Hinderer (ZT0550/551)
Jeremy Horton (TAC-4)
Benchmade (806 AFCK)
Emerson (CQC-10, Persian)
Chris Reeve (Mnandi, Insingo)
Trisak Jeeracheeveekul of Yuna Knives (Zen, Assassin)
I'm sure there are a few more obscure ones, but that's pretty much what pops up when I think of favorite folders...