I have to base this solely on my system, in no particular order:
-Centrafuse, yes I use others but CF is the easiest to use. Have to please the passengers sometimes.
-Mitch's HD radio cable
-iGuidance plugin for Centrafuse
Also, other programs I cannot live without which are NOT forum made:
-PDAnet (for iPhone), USB auto connect can't be beat. Why pay for separate data card when it's included with the iPhone.
-Slingplayer (now let's get a CF plugin!!)