Amain
losiparthouse
Stormer hobbies
Tower
Amazon
ebay
Hobbyking
Horizon
I do a lot of comparison shopping before pulling the trigger. Some places are much better for certain things. You get a feel after shopping around. When I want 1 or 2 small items it will be tower(Their coupons usually are useless unless you are buying big, and then you still are likely to beat the deal elsewhere) or if I need a tube of high pressure diff rebuild grease it will likely be losipartshouse.
Bundling up an assortment of parts, usually amazon.
The one off weird things usually ebay and free shipping is common there.