In reply to Somerville:
There is no one definitive guidebook because of the huge range of routes there are. It also depends on what sort of routes you want to do. Some guides focus purely on rock routes ( some of which may require glacier travel or mixed ground to get to and descend from and some are abseil descents enabling you to leave sacks at the bottom ). Some guides focus on mixed / snow / ice routes and some have a mixture. There are also guides that focus on higher quality routes in the general area, not just on Mont Blanc.
Your profile suggests you climb at a high technical standard and have done some winter climbing too. So here are some suggestions:
Mont Blanc - easy ascents in the range Probably too easy / not enough variety
Mont Blanc - five routes to the summit Good if Mont Blanc is your main goal / most routes not technically hard but need proficiency
Mont Blanc Range - classic snow ice and mixed Laroche and Lelong Not just Mont Blanc but has a broader range of routes which you may prefer
Snow ice and Mixed Vol 2 Damilano Much more comprehensive book, no rock routes though, great photos to help understand the layout of the range
Mont Blanc the finest routes Batou Large coffee table guide, covers the range not just Mont Blanc, rock and mixed routes. Lovely book and good intro to range. Routes from fairly straightforward to nails!!
Mont Blanc Supercracks Rock routes only, covers the range not just MB, routes all F6a and harder. Glacier and mixed ground still involved in getting to / from routes
Mont Blanc Classic and Plaisir Selected routes, rock / snow, ice / mixed. Doesn't just cover Mont Blanc. Routes up to around F6a. This is the one I would personally recommend as a starting overview.
There are other guides, some of which are very out of date but can still be useful, Eg Alpine Club Mont Blanc volumes 1 and 2. As a rock rat you may like the Piola rock guides. They cover the broader area, not just Mont Blanc.
In the Office d'Haute Montagnes in Chamonix you can study a library of routes / guides and can photocopy a limited amount too. That's also the place to access up to date route information.
Enjoy
