Bleau is a very popular bouldering area. The problems are organized into circuits and each circuit is color coded for their degree of difficulty. The color/difficulty codes are White/children (pour les enfants), Yellow/easy to a bit difficult, Orange/some difficulties, Green/some difficulties, Blue/Difficult, Red/very difficult, Black/extreme difficulties. School children are often bussed here to frolic amongst Bleau's many boulders.
The area is expansive and lies in the forest outside the town of the same name. There are about 15 different sub-areas most with many of other own other sub-areas. Many of the larger areas have as many as 5 circuits within them. That's a whole lotta bouldering, folks.
A terrific & exhaustive resource for Font bouldering is www.bleau.info. My wife and I stayed there during the summer of '06. Feel free to drop me a line if you are travelling there and have questions; hopefully I can answer them for you. Naturally, it's the best fricken' bouldering I've ever done. Of course, if you go during summer, you may expect to get spanked due to sweaty conditions. But who cares. Believe me, higher temps don't stop the locals.
Minor correction - bleau.info, no www in advance. It's almost redundant to add the routes to this site; the locals have already put them on bleau.info. Plus, the site is (mostly) in English, and comes with pics and even videos of various problems (useful for scoping beta on problems you can't figure out).