I was in a similar spot last year and decided to try some refurb stuff from Newegg and other used goods from ebay.
My experience is generally positive. The refurb mother board I got from newegg was wacked out because someone apparently had tried to OC their processor, which caused the board to malfunction in a way it would not boot up.
I just reset the bios and away she went. 40 bucks for 80+ dollar mobo. (It also did not come with the extras that most mobos come with, like PATA\SATA cables and the like, but overall I saved big time.)
After that mobo shorted out due to some misfortunate circumstances I went on the cheap again and bought a used Intel Media Series DG965WH from ebay for about 60 bones (around half its retail price). The guy I bought it from included EVERYTHING it had come with as well. It works like a charm.
Both of the harddrives I have in my computer I also bought used from ebay. I had a refurb pentium 4 from newegg for a while that ran fine (Did not come with a fan though, luckily I had a spare one). I have a gig of used PC2 5300 kingston ram as well, I got it for half off on ebay. Works like a charm.
Those are my experiences at least. I buy used when I think the deal is right and my chances are good. I would reccomend the same to anyone.