I've been trying to a build a new computer for almost 2 years now but every time I get all my parts picked out, I end up going on a military deployment so I put it off till I get back. And then I spend the next 4-6-12 months sifting through differnet options and researching out the parts i'm going to buy when I get home. So here's what I've learned:
Newegg is probably the best site out there for cheap computer components if you're going to build it yourself. I'll caveat that with Pricewatch.com is sort of like the Amazon of the computer world. It gives you the cheapest price from mulitiple websites. (usually Newegg and TigerDirect are going to be the winners) Amazon gets lucky every once in a while, but if you start mixing in the combo deals from newegg and in many cases free shipping; newegg ends up still being the better deal, even if the base price is $5 cheaper on Amazon.
The best time to buy: Black Friday (the day after thanksgiving) - Christmas. I was afraid after the new year, new parts would come out and my old parts would drop in price significantly by spring time. That wasn't really the case. It took about 8-10 months for the prices of my parts I had picked out to reach their holiday "sale" price as their normal pricing.
Software however, Amazon.com by far. You'd be super hard pressed to find a site with cheaper games.
Anyway, long story short, if its after thanksgiving and its on sale, go for it!
Hope this helps