In reply to clipskipper:
The Aig. du Tour from the Albert Premier hut is basically just a glacier walk with a short scramble at the end and at 3500m is a good first acclimatiser.
The Milieu Glacier on the Aig. d'Argentiere is a little harder, still not much more than a walk but a bit steeper at the end at 3900m.
The NW Face of Mont Blanc du Tacul is again a steep glacier walk and getting a bit higher at 4250m but with caveats regarding snow stabiltiy and serac conditions (enquire in the Office de Haute Montagne in Chamonix for the latest beforehand) though if you're planning to climb Mnt. Blanc via the 3 Monts route you'll be doing this anyway.
I'm sure there are some other walk ups to the south of Mnt. Blanc (Aig de Tre la Tete perhaps?) but I don't know that end of the range particularly well.