Amazon or Newegg

i order all of my pc parts from newegg. they normally have pretty good deals/rebates and i've never had any trouble with them (i've probably pushed 6K through them by now)

granted i've never really had an issue with a part received as doa where i needed to rma so can not really comment firsthand on dealing with customer service.

i also use amazon quite frequently for other things (mostly buying movies and series) and their shipping (from amazon directly not one of the sellers on amazon) is always super fast and i've never had a shipment packed wrong, come late or have an issue in any way.

ebay is worth a look once in awhile too. $79 windows 7 on there right now where the profits benefit a charity. sometimes you find other deals on there as well so its worth a look. good thing is that ebay has your back (just like amazon does if not buying from them).