The Kaffee Kränzchen is my favorite café in the Rheingau at the moment. It's located in the town of Walluf.
The interior is decorated in a lovely way with antiques - a bit like a "Wiener Kaffeehaus". The owner collects old cups so when you get your order, everyone will have a different cup from her collection (same with the plates). She also bakes all the cakes herself and they are extremly yummy!!!
So whenever you come to the Rheingau, don't forget to stop by!