I use an i3, 8GB of ram on an H61 board and ESXi for my "production" vms at my home. ESXi is quick to install and easy to setup, I would give it a shot first and if you don't like it, deal with the more time consuming setups on the other platforms.
Only thing to watch out for is whether or not your onboard nic is supported. You can either look it up online or take the "easy" way out and just order one of these with your components:
http://www.newegg.com/Product/Produc...82E16833106033
You will never regret having a good nic for VMs, even if you end up running one of the other platforms.
Oh yeah, SSD is a super-awesome investment for a virtualization box. I had 12 students simultaneously build server 2008 VMs from an iso file on the same SSD (a samsung 470 128GB) and the builds were logged into within 10 minutes. One student whom I dedicated a Seagate spinner to had the build take over twice as long with the same ISO file. So, a Crucial M4 or Samsung 830 will perform even better.
I guess, other than that, I would encourage you to get a motherboard with four ram slots if budget allows. Start with a minimum of 8GB of ram. I would also seriously consider buying just one 8GB stick now so that you can achieve high density as budget allows in the future.
Obviously, that's just my $.02 and there are going to be a multitude of opinions here. It is a little hard to go wrong as long as you buy a VT enabled processor, minimum 8GB of ram and an SSD though.
If you find yourself needing help with initial ESXi setup (like how do you simply build a VM?) post here or PM me and I'll be happy to assist as I have the time. The VMware community forums are a ridiculous wealth of information as well.
Since the VMware site can be a little confusing, you can get free ESXi right here:
http://www.vmware.com/products/vsphere-hypervisor/overview.html
you'll want something that will do nested vms that has made a lot of testing very easy.
VMware Player or ESXi is very good at either of these. And their price is right, and there is plenty of documentation on how to do it out there.