I just bought a 120gb hd for 40 bucks on ebay. WD 7200rpm 8mb, but it was refurbished and the guy didnt post it. It works fine. I bought a new 250gb wd 7200 8mb on ebay for my brother and as stated it was new and sealed. It came packaged in peanuts and was reasonably safe. Again, it worked, basically what I wanted.
I buy certain computer stuff off of ebay, stuff that is tougher than normal, or able to pick up dirrectly from the person. Mostly I look at feedback, cause if someone gets a 60 dollar paper weight, they are gonna be pissed.