There are 2 campsites in Bourg Saint Maurice plus one in Seez, which are all handy for the funicular to Les Arcs. If you base yourself in Bourg for a week or two and have your own transport, you can ride a whole bunch of different areas.
Les Arcs (obviously) – fun DH course and bike park, some decent waymarked singletrack, a whole load of un-waymarked singletrack!
Sainte Foy – up the valley about 15mins from Bourg. Lots of marked and unmarked singletrack. Generally very natural and flowing compared to other areas in the valley.
La Rosiere – waymarked stuff is pretty dull, but there's some excellent singletrack going back down to Bourg.
La Thuile – over the Italian border from La Rosiere (drive over or park up at the Col and ride down). Some excellent waymarked singletrack, steep & twisty.
Tignes – 6 DH tracks plus some decent (if a bit variable) singletrack.
All of the above have uplift of one kind or another. You can also ride La Plagne of course, but I don't know as much about the trails over there. Drop me an email if you've got any more questions.