I've averaged around $600 to $800 or so a year in pc part purchases over the past decade
most of that from newegg
I agree with gevorg amazon is very competitive, free shipping many times also.
I look to amazon before making any newegg purchase
buy.com is also worth a look, they just don't have as large of a selection of pc parts
originally I just used amazon for buying books and such, but they've got most everything now (car parts also)
newegg was only $2 cheaper on my most recent PSU purchase (yesterday)
but amazon is cheaper on an SSD i'm looking at by $15
competition is good, to keep them honest