Thanks Stacey, beat me to it.

Grab-Ons are/were closed-cell spongy tubes that you'd slip onto your handlebars.
Quite comfortable, but fugly as all hell. Initially, they were thicker than the ones in the pic above, IIRC.
They also made some grips for motorcycle bars. I picked up some for my sportbikes, but the fit was poor and they split in half weeks later. Luckily I wasn't riding at the time. I doubted their durability and abandoned them. Recently, I took a spare set and applied them to my GF's Trek 830 ATB. They fit a flat bar very well, and held up so far. She loves them. I had to admit, more comfortable than any of my rubber grips.
According to Harris Cyclery, the company is still around and make a set for drop bars.
If don't mind the geeky look, try em out.