For mine (and from what I can see, Heather's is about the same), we did a 100 box chart and for every book read, he gets a sticker in a box. Had to be a different book each time, which was a challenge for him since he likes to read the same one for a few days in a row. I would write the name of the book right on the chart. That become hard to reference back after 50ish, so I ended up putting it on a spreadsheet and alphabetizing (yes I did a spreadsheet

). Once I did that, I seperated the read books in a different pile. Next time, I'll do that from the start and avoid the spreadsheet.
It was cool, because it brought him back to books he hadn't looked at in awhile and introduced him to some of the new ones I had bought but he hadn't bothered much with.
The "prize" was his choice and something we picked when we first got started.