Hi A S,
The most improvable part on the verbal section for most people is the sentence correction section. I would get the Manhattan GMAT book and read it several times. I've seen that some people like the SC flashcards from BTG as well.

As for the reading section, it would be good to read a strategy book that
1) shows you how to take notes or map the passage
2) shows you the common wrong answers
3) shows you the common question types

I've gone through the Manhattan book for this and thought it was ok, but not excellent. You may be better off finding a tutor for additional help.

As for the critical reasoning, I actually like Kaplan's book about this section because it's concise. However, there are other more in depth books like the CR bible.

After you read some strategy books the most important thing you can do is practice and learn from your mistakes. When I say practice, I mean that you have to read and review for at least several hours a day if you want to make a major improvement on your score.

Good luck!
Dan