Amazon and newegg are my favorite online retailers.
Although, lately I've been leaning more towards Amazon due to Newegg's changes in business policies lately. Some of the customer reviews have me wary. I purchased my last graphics card through Amazon due to the issues I read about with Newegg's policy on RMA'ing cards with the 'free' included games.
Additionally, because of my location, I like tiger direct. They have 2 or 3 stores in my city. I prefer Amazon/Newegg to them, but if I need something right away they're my next choice to amazon due to price!