http://www.ebay.co.uk/itm/Mens-Tungsten-Carbide-Ring-Black-Carbon-Fibre-Band-Wedding-Engagement-Gift-/171186560585?pt=UK_Jewellery_MensJewellery_MensBracelets_GL&var=&hash=item27db839e49
I don't want tungsten carbide, it's a pain to find munch else though. It's really strong, but brittle and although it would take a lot to break it whilst wearing, a drop on the wrong floor can cause it to shatter or break.
It also can't be resized, so I'd have to buy a new one if my weight ever changed enough to affect my fingers.
Currently looking at stainless steel