Okay, so I'm sorry if everyone already knew that this was a thing. Or if you just think that it's dumb. But I just found it today and wish I'd had it years ago, so I thought I'd share!
In exchange for your email address, these lovely chaps and chapesses will help you find Kindle books for cheap. I've just spent a couple of hours feeding the site my Amazon wishlist (it automatically filters out anything that's not an ebook), tracking my favourite authors (hello Neil Gaiman, Margaret Atwood, Kazuo Ishiguro and Diana Wynne Jones!), and setting up a list of books I want that aren't yet on Kindle so that I'll be notified if a Kindle version is ever released. Plus you get to decide how much you want to pay for each title, and it will only email you once it reaches that price - or you can put in the percentage discount that you want. Amazing!
And it's especially fun on Chrome. There's a little extension that allows you do all this stuff while browsing inside Amazon. And little charts pop up to show you how the price of a book has gone up and down over the months/years. Fun! I'll probably now be getting a zillion emails a day and spending even more money than I already do on books (damn you One-Click!) but it's super addicting. This is totally virtual me right now:
Look at me with my glasses and my artfully tousled hair, being all virtual library girl!