, there was a $4500 rebate for 04 model. Dealer also gave me $1500 coupon (I don't know what was that). So, I got one (with 1SB and XM radion, sunroof) for only $16400+tax+fee. But that was the end of 04 and the one I got was the only 04 model left in dealer's parking lot. When I got it, I noticed my car had been sitting in this dealer's parking lot for more than 6 month(only 27miles though). So that might be the reason they want to kick it out at cheap price.
Two seat mounted side airbags added to 05 model(option 1SB?). I will not be surprised if it is a little more expensive than 04 model (mine only has curtain bags)
I think GM just "rename" its rebate to employ discount and I am not sure whether there will be more rebate if you wait for a couple of months.
Go to edmunds to see how much other people paid.
good luck