The only flavors of these I can personally attest to are:
Orange - added at end of the boil or in secondary. No problems here.
Vanilla - one bean split down the middle, added to secondary for slight hint of vanilla. Pecans - lots of oil kills head retention and improperly cleaned fresh pecans led to so much astringency in my Pecan Pie Porter it was almost undrinkable past the first few sips. If I did it again, I would use pecan flavoring.
perhaps a line of single hop IPA's - there's so many new hops out there!!!