If you want one that reads like a story, you might consider getting “On Writing” by Stephen King. It’s a good book and a great resource. I’ve also used a couple others but they were too dry to get any information out of .
I use the “Chicago Manual of Style” – an exhaustive reference. There’s also Strunk & White’s “Elements of Style” and Robin Williams’ “The Mac is not a Typewriter” if you’re looking for a smaller, paperback source.
My mom gave me the strunk and white book for graduation. i was not impressed. instead I usually use the Chicago Manual of Style Online. I would definitely characterize it as definitive. (heehee)
You should check out Grammar Girl’s blog and podcast. She handles mostly little grammar issues that are nagging or that pop up on a normal everyday basis. Here’s the link
Merriam-Webster’s Concise Dictionary of English Usage. Instead of laying down intimidating right and wrong rules, it presents the evidence, and lets you make up your own mind.