Ive seen a couple of hard drives for this purpose. Im not too sure how well they work.
The flashtrax (http://www.smartdisk.com/)
runs from $400 to $600 for 20gig, 40gig, 80gig drives. It has a lcd screen so you can see your pictures.
There is also the imagetank g2 (http://www.grand-level.com.tw/english.html)
an 80 gig hard drive that runs about $380 at newegg.
Both support CF cards. But i dont believe they are worth it for that much money. You will probably be better off buying many cf cards... or even one of the newer 1gb cf cards if your camera supports it. Shoot you can probably get a cheap laptop for that money.