Get a 1TB USB hard drive for $74.99 shipped
This is probably more storage than most users actually need, but if you're into video editing or want to a make a full-system backup, this is the USB-drive deal to beat.
Got storage? Got lots of storage? Newegg has a Hitachi 1TB USB external hard drive for $74.99 shipped. That's one terabyte for those not up on their techno-breviations.
Two caveats. First, there's a rebate involved (PDF). You'll have to pay $99.99 up front, then wait the prerequisite 8-10 weeks for a $25 bailout--er, rebate--check.
Second, the drive is formatted for Macs. That's obviously not a caveat for Mac users, but the Windows crowd will need to reformat the drive. It's an easy process (scan the user reviews for instructions), but it might take a couple hours.
The drive itself is a 7,200rpm Hitachi H31000US (read: faster than the 5,400rpm drives you typically find in USB enclosures) housed in a silver, monolith-looking tower. I know, I know, SATA drives are way faster, but how many desktops and notebooks have eSATA ports? Very few.
(Speaking of speed, if you end up using this drive with a Vista system, I recommend installing a utility like TeraCopy, which makes file copying go much faster.)
The rebate offer expires this Saturday, June 13, so if you're looking for a mountain of external storage for the lowest price I've seen to date, don't wait. Newegg tends to sell out of stuff like this.