If you can get ahold of 'Ryan Fees - 6maxNL Strategy Guide', it's a very good read.
Professional No-Limit Hold'em: Volume1 by Matt Flynn, Sunny Mehta, & Ed Miller
This ^ is a good read & is highly recommended by many cash game players.
You could also check out Harrington on Cash Games (as mentioned by others). I read them & didn't find them all that great to be honest (not bad but not quite what I had expectations for. I believe this was in part due to all the hype & build up I'd heard about them, AND, because when I first got going with nlhe Tournament play I read his Tournament Play books and found them to be very good (at the time,... and for sure a great base for anyone getting started in tournament play).
I'm not a cash game specialist at all (have had a go at playing it for awhile online but it's not my preference)... so my recommendations might not be the greatest but are pretty much what I've read myself & what i've heard many others suggesting.
Another book to consider is No Limit Hold'em: Theory and Practice.
Might be an idea to check your local library for any of the books mentioned above. The library in the town I live in will get most books for me via an inter-library book loan.
There's also some excellent articles/strategy guides to be found online if you hunt around for them.
Brad Booth - > "Like a fight... it's not how you start, it's how you finish"