Pay less than invoice, if a dealer will not go that low, walk away.
The MSRP on my truck was 38,200
I paid 30,800 ($300 under invoice -$2500 rebate, and -$500 farm bureau rebate).
My only other advice is to spend a lot of time on the Dodge site, fooling around with options to figure out which ones give you the most value. IE, if you wanted an 04' SLT with fold flat seats, you must choose premium cloth seats, and also choose the fold flat option (about $400 total), but for only $900 more you can get leather, which come with fold flat seats included. You end up with an interior that looks similar to a Laramie, but for way less $$$, not to mention none of that other automatic Laramie climate control crap to maintain down the road.