Montgenevre is good, les orres is small and busy (not that good), serre chevalier looks good but not ridden there.
Further south: Allos is excellent, Pra loup is ok for a day, chabannon (?) is meant to be good, super devoluy is pretty good for a day or two and orciere is excellent.
There is also vars, not ridden there but i have had mixed reports.
Check out big bike magazine website and http://www.26in.Fr, both have bike park guides.
Have fun!