Nice Used Amazon/Greasemonkey Script

If you buy used stuff at Amazon, this script alone makes Greasemonkey worth installing. Amazon TotalUsed tacks the shipping price onto the lowest used price so you can see how much savings you'll really be getting (it assumes, of course, that you always boost your Amazon orders of new items to $25 or more to take advantage of free shipping):

Especially handy for me, as I always tend to look at the pre-shipping used price and think "what a bargain!" before being ultimately deflated upon purchase.