I've done my online shopping through Nashbar for misc parts (bars, stem, seat, seat post, tires, etc...), Ribble for my groupset (and headset since my bike has an odd sized 1' threadless), and Probikekit for misc kit, water bottles, and some other odds and ends. No complaints about any of them. Oh, I bought some shorts off of Performance once and they were inexpensive and they are fine, but the shammy isn't good enough for extended rides over 20 miles.
Add Wiggle and ChainReactionCycles (CRC) to your list, both UK based, but both send internationally, the UK has an extremely competitive bike market, and prices are normally (German shops can be cheaper for some things) just about the cheapest in the world, take the VAT off, and you get it even cheaper that we do in the UK.
I usually buy tires, tubes, chains, and assorted bike parts from Niagara Cycle. Their prices are very competitive. I formerly used Nashbar but they seem to have dropped a lot of items I bought there in the past. If you need a single, specialized component either eBay or Amazon often will have them when they are hard to find elsewhere.