I'll second the Blue Jean's Cable & Monoprice suggestion.
I use Belden 12 ga from BJC with the compression banana plugs from Monoprice for my center and rears (6', 25'). No fit problems what-so-ever and it looks great. My only complaint with the Belden cable is that it is somewhat hard to work with because is a pretty firm cable and it likes to wrap up on itself - it's difficult to get it to neatly lie on the floor.
One thing to consider is that if you are going to run the speaker cable in the wall, the Belden wire is UL/NEC rated for in-wall use. A spool of lamp cord may not be. Some folks care, other's don't. Just an FYI.
