Misco, Morgan, Retek and AUT direct are the places I look for bargains. Morgan haven't had any good graphics cards for a while though. Retek seem to have ATI only, but some of their reconditioned cards are great value if you can live with a recon card and a 90 day warranty
Failing them, you could consider Ebuyer, Dabs or Novatech own label cards; same cards as the named manufacturers but without fancy coolers, stickers, freebies etc. Check the respective warranties though.