You've got near top of the line parts across the board. Should you need/want o save money, it is certainly possible without sacrificing any noticeable real-world performance. ($300 or so in memory and mobo, eg.)
12 GB of CL7 1600 is overkill in several ways lol. 6GB of 1333 CL8 would be OK. Yours will benchmark better, but you won't notice better gaming.
850W is plenty for future crossfire, and that specific Corsair is top of the line.
The raptors will work. However, you could improve overall system performance noticably by going for an Intel X25-M or OCZ Vertex SSD as your OS and primary gaming drive.
Article here:
http://www.anandtech.com/storage/s [...] =3531&p=31
Excerpt:
"While I wouldn’t recommend any of the JMicron based drives, with the Vertex I do believe we have a true value alternative to the X25-M. The Intel drive is still the best, but it comes at a high cost. The Vertex can give you a similar experience, definitely one superior to even the fastest hard drives, but at a lower price. And I’ll spare you the obligatory reference to the current state of the global economy. The Samsung SLC drives have come down in price but they don't seem to age as gracefully as the Intel or OCZ Vertex drives. If you want price/performance, the Vertex appears to be the best option and if you want all-out performance, snag the Intel drive. "
The cooler is fine.
The 5870 is the right top-of-the-line card to buy today. The 5850 would be more than excellent if you can wait two weeks or so.
On-board audio satsifies most of us quite well. Try it, you can always add an audio card later. I doubt you will unless you have some very specific audiophile requirements.