Something I have tried this week is Goodreads.
I have known about it for quite some time but never took the time to go and do it. I just set up an account and added a bunch of middle grade books that I could think of as well as a few personal reads. I also added one of my teacher friends and browsed through her books to see some more that I had not thought of. I primarily was doing it with the iPad app. I searched some titles by name and others by author (if I knew I had read a few by them). I also used the scan option to add some from my summer reading pile.
I probably need to search around for some more teacher friends to get some other good suggestions but at least I started.
This past year I had my students using Biblionasium which I thought was great.
You create a class and add your students (with lexile levels if you want). At first I created two classes for my morning and afternoon. Once I got into it a bit I decided I would rather have one big group so they could interact with each other and so I didn't have to add everything twice.
Once in they can select their avatar and add their own books. They can rate books and recommend them to classmates. They can enter the books on a reading log and get "awards" for various things like different genres and number of books read. Students can also see each others shelves to get ideas without specific recommendations. I did add myself as a student as well as a teacher so I could set up a student shelf with the books I was reading.
As a teacher I could add required and/or suggested books to a class shelf for students to reference and add. I could also track all sorts of things like logs, awards, book levels, etc. I could also create specific challenges for the class, groups, and/or individuals.
I would highly suggest checking it out.