Depends on what you're expecting & likes/dislikes. Do you want to stick w/headers, or true dual? Is 2-1 your bag (better performance)? Chrome or black...you get the point. Agree w/ncsteve - go to some bike gatherings, look, listen & ask. Then set a price & go for it...good luck!
+1 of the true duals for performance and sound and V&H for quality and service. Also the set will keep the heat away from your right leg. You can check YouTube for samples.
Good Luck!
Depending on how much you want to spend - with our 07 Ultra we went with V&H oval slip ons and kept the stock head pipe- Just got a 2011 Street Glide and sat around the dealership all weekend listening to bikes come & go -- ended up buying Rinehart True Duals-- went w/ true duals on the 2011 in order to have a clear head pipe - which isnt a worry on the 07. Best bet is to hang out and listen to the bike in person so you know exactly what sound you are looking for