Spool Holders

Makerbot Replicator, Replicator 2 and Replicator 2X

Spool holder for Prototype Supply filament (by ToyBuilder)

http://www.thingiverse.com/thing:77261


Free-standing Spool Holders

Filament Server System (by JuliaDee) 

http://www.thingiverse.com/thing:151440

FeederBot Spool Rack

www.feederbot.com