In reply to MikeLell:
The MBU pass is well worth the money if you do the Vallee Blanche or ski regularly from the top station of the GM. But if you don't plan on doing this, then the Le Pass is the way to go.
There's plenty of good skiing on Flegere and Brevent and from Herse and Bochard on the GM.
I got the La Pass for 4 days last year at the start of a trip as i wasn't planning on doing anything too serious at the start and then the MBU for 6 days after a day off.
I think I paid about 27euros for a single to the top of the GM on one day when i had the La Pass. But the price may have gone up this year, have a look on the compaigne du mont blanc website.