I feel like I have a good working knowledge of the small stakes book--it helped me become a winning $3/6 player. What do I read next, as I would like to move up to 5/10 and 10/20 someday in the future?

I know 5/10 is still considered 'low limit' generally, but I've heard several times that the 5/10 games around where I live are pretty tough. Thanks for good input on a not so good question.