Just found these guys the other day looking for some chainrings:

www.branfordbike.com. Interesting selection of bike parts and good service.
I always check www.rei.com for closeout deals.
Great service on tires from www.biketiresdirect.com.

Am surprised that no one has mentioned Wallingford Bike yet -- famous for their 6-month return policy on Brooks saddles, plus racks, bags, etc. I have never bought from them (they always appear to have a lot of out-of-stocks) but I know lots of BF people seem to like them.