My amazon wishlist is full of nerdy things, but one of my favorite nerdy things I ever put on there was the PageKeeper.
You clip the clip to the back page(s) or cover of the book and then put the little wire arm on the page you are reading. As you flip pages it keeps your place with the wire arm. So for someone like me that loves to read in bed and then falls asleep, this is basically the best book mark invention ever. Now when I wake up my spot is marked and I don't have to spend 30 minutes looking for where I left off before I fell asleep and dropped my book on the floor.
If you still read regular books or you know someone that does, this is awesome and you should get it.