I would say ebay but I also will not pay more for needles including shipping and handling if I ran down to my LYS or craft store to buy them. I just got some addi needles on ebay a lot cheaper than at my LYS and I got to pick the sizes and the lengths I wanted them to be.
http://cgi.ebay.com/6-Pair-ADDI-Prem...742.m153.l1262