I purchased
All My Books to keep track of my ebooks.
I keep all my books on an external 500GB hard drive and use All My Books to manage them. What I really like about it is I can click a link and AMB will search a number of sites for details and plug the information in for me. I can also open the books directly from AMB in case I want to look at it without copying it to my reader. I no longer forget what I've already purchased which is a big plus for me.