I don't buy too much stuff that I don't really need. I get a fair amount of stuff at the LBS - the relationship really pays off when they know me and know my bikes - and I feel like a celebrity walking into a store and being recognized
I don't resist a good sale on stuff like tires at Performance or Nashbar, and I cruise the sale stuff at TE too (got some of those Zoic knickers - sweet!) but except for the occasional blender, try not to over-accessorize my bicycle. I like Sierra Trading Post, too (especially for the camping kinds of things for the yearly long tour).