Over the past 10 years or so, I've become a big fan of
http://www.torquetechexh.com/ They even sell a 3 1/2 inch system which wraps over the axle and really drarwf's the 3 inch systems that everybody seems to have these days. I've installed a few of these systems and let me tell you, if you got a decent rat motor up front, that 3 1/2 system really thunders!