Thule is the only one who makes roof mounts that attach to the OEM BMW roof rack mounting bolts
Also is the Yakima Viper the way to go for MTB and road bikes?
Don't forget that BMW also makes OEM roof racks too (hence the term "OEM" ). Surprisingly, I find the OEM Profile 2000 stuff to be cheaper than Yakima or Thule when bought from a discount BMW dealer (e.g. Crever BMW, Pacific BMW or Circle BMW). I personally use Crevier and find their prices and service to be top-notch.
Unless you are looking to add tons and tons of different attachments (Kayak, lumbar, etc.) you can go with the OEM solution. If you have strange and varied needs then you may as well go with Thule.
I have read from E46Fanatics that Thule is actually coming out with a line of attaachments that uses the BMW OEM "slot" so the variety may actually increase.
For an idea on prices, go check out eBay and the prices you see there are comparible to the discount BMW dealers.