Looking to upgrade to Mac Pro; help needed

[mac000]

I'm looking to upgrade my 2.4 C2D iMac to a Mac Pro, however I don't know where to start. I'd like to possibly purchase a used system and am wondering if I need the quad core or older dual core Xeon Mac Pro.

Where could I find a nicely configured Mac Pro and what should I be looking for in configurations to last me 3-5 years?

 

[bntz313]

apple refurbished site, I got my macpro quad 2.8 for 1999

 

[iToaster]

I own a single quad 2.8 and it's great. I'd just go with it, the benefits aren't really apparent, but you'll be using it for the next couple years so you might as well go with the newer model.