I agree, both Seagate and WD are great drives; I have 4 of the Seagate ES.2 1TB drives in my NAS, server grade which equates to higher MTBF (mean time between failure) and presumably more robust hardware.
You should take into consideration what your needs are as far as space and speed as well. I ended up going with 2 150gb Velociraptors Striped (Raid 0) for my "System" partition and a 1TB Western Digital Black for the "Work" drive. The stock 320gb drive I use for my Windows setup (currently Windows 7 beta).
This setup suits my needs quite well, super fast boot/application drive and a very respectably fast data drive for projects.
For memory, I picked up 6 more 1gb Apple Dimms on eBay as well, pulled from Mac Pro's. 8gb was plenty for my needs and fully populating both risers is one of a handful of configs that give the best performance.
Hope that helps...