I have Royler Gracie's Submission Grappling book (with help from Kid Pelligro and Wellington Dias) and it's pretty good.
It has about 250 pgs and is well-presented. They present many different options (sweeps, defense, submissions) from various positions (mount, guard, side mount, etc). I find it most useful for learning specific moves. Like I've only been rolling for 2 months now, so I've used it so far as a tool to learn 1 or 2 different submissions from each position. The pictures are well done and pretty "illustrative", and the descriptions are thorough, making it clear what should go where and why. If you think about getting this one (he's put out a few books), make sure you get the one which is suited to your game (e.g. gi, no gi, etc.). I bought this one without realizing it was all submission grappling (i.e. no-gi).