i work for a relatively small appliance and electronics chain that's only in the great lakes region, and because of that, i'm only eligible for a few programs out there...
like other people have said, hpinfolab is awesome... i've gotten a pocketpc and 2 dvd burners for maybe 50 bucks out of my pocket for all three... other than that, i was eligible for retailaccess for a while and got some decent norton software for free, and one year i got in on the intel retail edge program and got a pretty good processor, mobo and a copy of windows for cheap.
that's just the stuff i was able to get in on being that i work for a relatively small retailer.... now with major retailers you've got more available to you...
microsoft's expertzone is a pretty good one to get into, easy quizzes and you can get xbox and pc games for really cheap (like 6-10 bucks each) as well as accessories... also, you'll want to check out retail access, you can get what's called NFR (not for resale) copies of the latest symantec software for free...
aside from those, you should be able to talk to the sales reps for the manufacturers of products you carry... many of them offer "accomodation" sales where they will sell you their products for way cheaper than you could ever get them.