X9SCM-F Supermicro motherboard, Kingston ValueRAM 2x 4gb sticks. If your running Windows Server 2008 it usually idles at about 1.5gb of ram, and if your using the core version, then much less.
A 32 slot CS
server will use no more than 500mb of ram. Usually they use only 350-400, but we'll say it's 500mb just to be safe.
If you run four of those servers, you'll put one server on each core, and have a total of 128 players, and you'll be using about 2-2.5gb of ram. You can then add another 1-2 servers to run on the virtual cores, or hyperthreaded core (which will tap into any extra room on the 4 other cores) and now your at 3-3.5gb of ram.
I'd say go with 8gb, as you won't exceed that with Counter-strike servers (TF2, DoD
are all about the same as far as resource usage goes) And before you fill up 16gb of ram with Counter-strike servers, you'd max out your CPU, and possibly your NIC.
Now if you say wanted to do minecraft servers, then yes, go with 16gb. The 4gb Kingston valueram that fits in that board costs about $40 per stick, so it's best to get 8gb, and if you do need more (which you most likely won't) then just ship a stick out to your Data-center unless they charge quite a bit for remote hands.
As for processor, if your running 4-5 CS
servers, you could easily get away with the E3-1220, which costs about $200 ish whereas the 1240 is $265 and runs a bit faster than the 1220.