I use eco-tech degreaser every now and then and most of the time just wipe the rims down carefully with a bit of unoily rag. You can also get rim brushes, like a pummice stone for rims which are pretty good, if a little expensive.
Joe, don't use washing up liquid on your bike - it's full of nasty corrosive salt, just like the stuff you spend hours cleaning off your bike after winter rides when the gritters have been out.