Roederer Cristal. I drank two vintages today at BAFTA in London's Piccadilly (you can see the BAFTA 'mask' in the background of the picture) - the 1990 and 1996, from magnum. Both were utterly fantastic: fresh, complex and almost perfect, with the 1990 just having the edge on the 1996 at the moment. In time the 1996 may prove the better, but it's a hard call.
Cristal is famous as being the favoured tipple of hip-hop stars and gangsta rappers (see here and here, for example). It would be nice to say that it's overhyped, but it's not. This stuff is thrilling. Almost unbelievably good. I also tried the Roederer 1999 releases, my favourite being the Blanc de Blancs, which again is spectacularly fresh and vivid with lots of complexity. The regular vintage 1999 is also very impressive, with some more richness underneath the fresh fruit. Roederer rocks.