Veritas makes a dedicated RC book -- but I would keep the focus on quality over quantity. You can take two GMAT students, one who does 15 passages only, and the other who does 100 passages, and the former will get a better GMAT Reading score. Make sure "how" you read the passages and approach the questions really serves you.
Take short notes while you read. You can't possible remember every piece of information from the passage, but note-taking as you read will help you recall much more information than memory alone.
Don't skim. If you only read a sentence here and there, you'll never grasp the "big picture" of the passage. It can be tempting to rush through the passage to get to the questions more quickly, but then you'll be going back through the passage inch-by-inch, searching for the answers to those questions! Read at a relatively efficient pace, but read thoroughly the first time around.
Write down a Prediction. For each question (except for very specific Inference questions) you should be able to come up with your own answer based on your notes and your understanding of the passage. Trust that you can come up with a reasonable approximation of the correct choice on your own. Process of elimination is a much more effective method than simply reading and re-reading each choice.
Good luck!
