If you ride a Moulton, you clearly have taste. But the real test of your sense of style is in what you choose to adorn your bike with.
I love Nitto products, and this Bottle Cage made by Nitto, especially for Moulton is pretty elegant in Stainless Steel.
Available from Alex Moulton Bicycles, it's pretty expensive at £45.
Alternatively King Cage makes bottle cages in both titanium and stainless steel, for a much more reasonable $15.