apple, blueberry i've tried and work lovely with tobacco
off the top of my head-
caramel (ry4 obviously) but molasses or treacle type flavours might work
liquorice (maybe even red)
whiskeys or brandies maybe
I like it with the merest hint of liquorice, and secondly with maple syrup. This one needs a couple of weeks steeping to really bring out the maple syrup.