I don't know enough about specific products yet, but it seems clear Sandy Bridge really was the right choice!
Go for something like a core i5-2500 (non-k) and H67 based motherboard.
8GB ram (2x4gb 1.5v)
A 2TB hard disk (or 2x1.5TB and RAID 1 if you want hardware failure protection)
Don't bother with a discrete graphics card at the moment.
Get the usual solid PSU, case to taste, windows 7 x64 etc.
Then see if you've got enough left over for an SSD.