If your credit is decent, finance through GMAC for the $3500 off. Most of these prices assume at least that, as well as GMS (GM Employee pricing). If you are GMS-eligible there is another $1k available if you finance through GMAC. Though I'm not sure if they changed the $3500 to just a GMAC rebate, or if cash is available.
If you are financing, it's important not just to figure out the purchase price, but also the finance rate. Again, the GMAC rates of 0.9/36 months, 1.9/48 months and 2.9/60 months are pretty much unbeatable.
--Robert