Performance Configurations

Hey everyone, I need a little help setting up my system for best performance for my design machine.
I have an 8-Core 3.2 System, 32GIGs of Ram, stock 500gig HD*

So, I was thinking of buying another hard drive today.. But Then I got to thinking about RAID and SSL Drives..

How can I boost performance with a drive config, which drives and do they have to be matched sets?

I'd like atleast 1TB in this config.. more is better, but this isn't my main machine.. Should I just get another 7200rpm and make a raid set?
I have a great backup system so I don't want to mirror as I back up daily

I just want it to be as fast as possible without overclocking. HALP!

Any suggestions would be greatly appreciated!