mavic 717.... i here you can make them tubeless if you please... they are light and i have used them for a season of riding dh at diablo (in nj) on a beater hardtail.... i rode pretty hard too, yet the front still holds strong... rear broke after it fell a good 30 ft down a rock face
go mavic. they are strong and light. the only problem that i know of from them are spoke pull through. the only case i have seen though are on older well used rims.
i have also had pretty good results with sun ds-1/2. on is welded and it a little lighter. they are light and have held up well for me thus far and i ride fairly aggressively and weight quite a bit.
if you are light and ride light look into the stans xc rims. a friend of mine has the 29'er verson and he seems to like them alot but remember that they are light and probably will not last well in the long run. at the same time though they are light, very light.