This is the tool I use most. I have always used Amazon’s Wishlist. But it only has limited value as just a list. Since eReaderIQ.com/Pricewatch added the ability to import your Amazon Wishlist, I have a reason to really use the wishlist. In the past, if you save a Kindle book in the Amazon wishlist, your get a link to purchase options. But if you save a paperback or hardback, the price was listed in the wishlist. So I usually saved the paperback or hardback, even if I really wanted to Kindle version. But with eReaderIQ, you import your wishlist (only books saved as kindle version are imported), then the price at import, the current price, and the lowest price since you started tracking.
The best feature is that you can set a notify threshold. If you have a $9.99 book and you want it to notify you when it drops to $7.99, you set the notify level at $2.00 and give your email address. I tend to go look at the list every couple days because I am impatient, but you do get emails. My books are mostly theology and do not move much. New Releases and Fiction tend to move more often.
I do not want to encourage anyone to stop visit this blog, but the eReaderIQ.com/free section is pretty good. It get all the free books (shows over 900 when I am drafting this post). It will also email you when new free kindle books are up. There are a few reasons you might not want to use the free section. First, it is everything, so a lot of sample chapter and things that really are not books show up. Second, it is everything, so a lot of erotica, really bad independent books and just general junk has to be sorted through to find the good free books.