Love fictfact.com!! I've been using it for quite a while now. They recently upgraded the site, and I like it even better now. Like jersysman said--they are very responsive -- when I've reported a series they didn't have or books missing in a series, they've added them quickly.
Another great site for series information is
http://www.fantasticfiction.co.uk/ . It doesn't allow you to track books you've read, but has lists of both series and non-series books by author.