How much is that old Mac worth?

This is a cool site. mac2sell.net estimates the resell value of your old Mac. You enter in your specs and it guesses the value. I'm not sure how accurate it is, but it's a place to start when thinking about how much you might get if you want to sell (or how much is reasonable to pay if you want to buy.) My iBook G4 933 MHz is worth $440 according to them.