From my experience if you use Windows 7: Get the 64Bit version. Use 8GB RAM. Any reasonably fast quadcore processor should suffice (usually in the price range of 150 - 200 €/$ ). Just be carefull to get one which supports virtualization features if you want to run VMWare and such. In my experience this speeds the VMs up. I think both AMD and Intel a viable choice. In my experience for development work you won't sense any differences between similar cpus.
Get a fast system disk (SSD would be perfect but it's rather expensive (I wouldn't take less than 120 GB, 160 would be better). The new Samsung F4 with 320GB is very fast for an HDD and very affordable with about 36€). Get 2 and configure a RAID 1 if you need guaranteed (or rather almost guaranteed) uptime so that one drive may fail (which of course should then be replaced immediately and the RAID be allowed to rebuild).
For data almost any drive will do. Just get one with enough capacity for your needs. In my personal experience I had the least problems with Western Digital and Samsung drives but Seagate and Hitachi seem to be ok too these days. But since you code lies on a server in some source code management system which gets backuped regularly a failing hard driv with your source code is not to much of a hassle ;) Yep, that's a hint :)
If you need to choose between more RAM and faster CPU get more RAM. My VS 2010 doesn't use much precessing power (C2Q 9550 (2,83GHz, 4 cores) even when Intellisense doesn't react. I don't know what exactly VS does in those moments but going from 2C/2GHZ to 4C/2,83GHz didn't do anything to help in these situations. It sure helped for having more applications open in parallel.
Power supply? Well, beQuiet, Enermax, Seasonic, Nesteq. Any of these with about 500W (these company are very reliable in my experience). If you're going to put more than an entry level GPU into the system (basically anything current which is less than about 80€) you might need to check its power requirements.
For mainboards I sticked to ASUS. Usually very reliable. Don't use the entry level boards. A price point of about 120€ should be sufficient. Just pay attention to it supporting the amount of RAM.
RAM vendors I've had the least problems are Crucial, Kingston, OCZ. You don't need super fast RAM. In programming you won't feel its speed. Just get enough of it. Oh, its speed should of course match the selected cpu.
Case. Lancool is ok. Just see that it's big and deep enough.
My conclusion for the main parts: 8GB RAM (with appropriate 64Bit OS), 4-6 core cpu with hardware virtualization support, fast system disk(s with RAID), large enough data disk.