Answer
You're on the right track as my motto studying for the GMAT is study in print and practice online.
The only book I used was the official GMAT review books which can be found in almost any bookstore. I supplement that with online materials. Here is some to consider.
If you haven't already you can get free GMAT practice tests at the GMAT homepage. http://www.mba.com/mba
I also used http://www.bellcurves.com They have more questions, quizzes, tests with features to find your weaknesses. There is a free option you can try. There are also free GMAT lessons (no sign up) you can take advantage of. http://gmat.bellcurves.com/free-gmat-prep
I also went to http://www.beatthegmat.com a lot when I was studying. It is a great GMAT forum/ community where you can get more tips/ advice/ materials with a quick response time.
Hope this helps and best of luck.