Like Michael said, you could go with the Core i3. Another cheaper option if you’re on a strict budget is the new Pentium parts like the G620 I linked. You give up a little performance and some of the SandyBridge features, but it would probably work fine for your needs. There is a G620T that is also a 35W TDP part.
If you have the money, spring for the i3-2100 or i3-2100t.
I don’t have any experience with FreeNAS.
