cork and bamboo bar-end plugs from Portland Design Works. They look like miniature mushrooms and are so nice that I almost don't want to install them on my bike.
I like to use wine corks to plug the ends of handlebars, preferring their organic warmth to the cold look and feel of plastic and metal plugs. But I ran out of corks and didn't want to have to drink more wine - so I looked around online and found these delightful creations. They are practically weightless, if you care about that sort of thing, and are made in both drop and upright handlebar diameters. Just lovely all around.
Since my Rivendell no longer has bar-end shifters and my other roadbike is a fixed gear, I will probably order another set and install these on both. What are you using for bar-end plugs these days? I've tried lots of different things at this point, but keep coming back to corky/woodsy stuff - it just feels nicer.