I think Core i7 (as fast as possible based on the budget) with LGA1366 socket would be a good choice. RAM (2GB modules) is not extremely expensive, so I would go with 12GB and a motherboard that makes all this possible. 4GB modules are still pretty expensive so two sets of 3*2GB modules could be nice. LGA1366 based Core i7 processors have triple-channel memory architecture so two sets of three RAM modules should be a good combination. For GFX I also have to recommend nvidia for your usage because of the cuda. As you said, there is relevant software that can utilise cuda (e.g. Adobe CS5, 3D Coat and Octane render). The new GeForce 400 series seems to be running quite hot (which also means noise) and taking quite a lot power and it is not yet fully supported (at least not yet by e.g. CS5 Premiere Pro's Mercury playback engine) so maybe an older GTX285 could be a good choice. I would prefer Ati's 5800-series due to more modest power requirements and less noise, but as you said, at the moment, cuda may bring some advantage for 3D work.
For the hard drives, if budget allows, one might consider an SSD disk for system and software and a couple of more traditional spinning hard drives for storage and backup. RAID 1 configuration would give extra safety against data loss and RAID 0 would give better performance which might help e.g. with HD video editing. External hard drives, e.g. with external sata connection, can of course also help with backups and are easy to add later. I do not know, which are the best drives, but for some reason, all the 3.5" drives I have bought lately are Western Digital drives. At least to me, their present line-up had the most appeal.