I really, really recommend the Powerscore CR
Bible. It does an amazing job explaining each type of CR question and how to attack it systematically. If you're weak in grammar, I've heard great things about the MGMAT SC
Now for reading comprehension, I suggest you read voraciously (in English!). Anything goes: fiction (I'd choose Dickens over Sidney Sheldon), non-fiction, the WSJ, etc. You'll not only get a good sense of what good writing should be like (which will help you with SC and the AWA) but you'll also sharpen the habit of understanding complex texts. If you're really short on time, I would choose classics from the 20th century by authors like Steinbeck, Salinger, Hemingway, and their friends because the vernacular used in their work isn't outdated yet.
Many older classics are available online (Project Gutenberg, for instance) for free. If you're really going to focus on verbal only, you should just spend $50 or so on the relevant books. Read, though. Every single question type in GMAT verbal essentially tests whether or not you learned how to read and reason properly (even for SC; you're expected to know what a grammatically sentence looks like).
Life with the GMAT:
Jerome: Ben, c'est 20 secondes de plus qu'hier sur le meme parcours! C'etait bien le meme parcours la, non?!
Gigi: Mais t'enerve pas, Jerome, je crois que t'as accroche une porte.