I had a bunch of these left over from my recent wood floor project, and they worked like a charm:
They're cheap (well free for me anyway
), small & black (so they don't stand out) and tapered w/ little ridges so they wedge in and stay put. I'll try to take an actual photo and post it up (if I remember), but they worked great I think. You can find them at HomeDepot or any flooring store for about $5 a pack.