If you've got an iPad, or somehow ended up with Nook and a Kindle, web app Leatherbound could save you real cash the next time you're browsing for ebooks. It instantly compares prices on all three major ebook platforms.
Click the image above for a larger view; white-on-green button text doesn't screenshot all that well.
The app works in an instant search fashion, so it pulls up results as you type out each new search phrase. It's not all that great at knowing that it doesn't have results for you, so if you see the spinning search wheel for a good bit, assume it's not available in Leatherbound, or else their servers are under duress. When it does work, Leatherbound is a great, free comparison tool.