Somebody herein mentioned that the Kindle's every bookmark appears in the Clippings.txt file. I had wondered what all the lines in there were, since I hadn't clipped anything -- so thanks!
So now, when I have the Kindle connected via USB to my computer, I remove those excess lines to clear the Clippings.txt file ..... but I move them into a BooksIveRead.txt file. Reduce the lines to just one per book, and voila -- a quick way to store the title (and sometimes author) of what I have read.
Where the author isn't included, I add it. I also am trying to include the date of publication of the book, just for future reference.
If you like to keep track of stuff that you've read -- try this technique! I have a similar list from my Palm PDA's for the past 10 years, so now I'll keep a list about my Kindle.