I thought I would toss my 2 cents into the ring. I use an excellent app called
"My Book Droid" available in the Android Market. The free version will hold up
to 50 titles, the full version is only a couple of bucks. You can add books by
scanning the bar-code or ISBN number. So far the majority of my library have
been in the database. You can also edit/enter new books and the app connects to
Amazon, Goodreads, and Google. It can also generate lists to keep on your PC. I
do not know if one exist for I-phone, but for droid, it works great. I love it.