I just got a set of oversized Aluminum grips for my Ducati Motard. I had to trim the cam a little to get to work with the Ducati, but I've very happy with the quality of the parts. I got them from MotoCyco (the same company that makes the Grenade Brake reservoir).
http://www.motocyco.biz/
I have a set of Harley-Davision grips on my Ducati Monster. The H-D grips are for a 1" bar (made of hard plastic), so I had to use a inset tube (the insert tube is 0.875" ID & 1.000"OD) to mount the left side. I cut the cam off the H-D throttle side and slipped it onto the stock throttle tube (siliconed).
The H-D grips are 1.5" OD ($80+ USD) and the MotoCyco grips ($125 USD) are 1.375" OD but are direct replacements.
I put oversized grips on the sport bikes because I have Tendonitis is my right wrist. The large diameter feels better on longer rides (I have the standard rubber grips on my track bikes). With my heavy leather riding gloves on I can't really tell any difference in the soft rubber and the hard grips.
I wanted to see what everyone else thought on the subject.