1) Look around for those "awesome" things everywhere (craigslist, amazon, ebay, pricegrabber.com, sams club) before buying retail.
2) Try to hold of purchases as long as possible. You are paying for purchasing excitement. kmull is right, most of the items that are retail won't be worth much in a couple of years. I can buy all the Command and Conquer games now for $50 but I have spent nearly $500 on them over the past ten years. I am not saying you should always hold off on all purchases but you should generally hold off on a lot of them especially digitalized entertainment items.
3) Play the crap out of what you own. Now that you own that DS game, play it too death!!! Also, instead of watching TV (more stuff you don't need) or checking out internet ads, play as much PS3 with your GF as possible. Make a rule that you will beat a game at least once or watch a movie twice before buying another one.
4) Check out old entertainment! I love old games and just don't have the time to invest 40 hours just to "learn" how to play a new game. Old games, movies, and music costs much less than new stuff.
I would consider myself a very savvy shopper, I definitely research and get the best price. I do hold off on buying things, much longer than the "1 day per $100" rule. I don't have a problem with buying used, however I generally have a rule against buying big ticket electronics used. The same goes with new games. If a game is very popular, it will not show up used for a low price on craigslist or ebay, usually only 5-10 dollars cheaper and quite a few months later. I've been waiting for this particular DS game for about 3 years now, ever since I lost the prequel.
I definitely do play the crap out of everything I own, I don't have to worry about that. I have 420+ hours on Orange Box, the last computer game (set) I purchased. The DS game I bought (Final Fantasy Tactics A2) promises 200+ hours of gameplay. And I play the PS3 with my gf everyday to de-stress her and get some entertaining activity together that tests our communication and teamwork... and we don't have cable/satellite, so our TV watching is 1 hour max watching the Daily Show and Colbert Report on Hulu.