Exactfit belts are a popular choice. I have a pair which I'm about to fit on my 1100 Evo. They are considerably cheaper than OE Ducati offerings (£85 per pair as against £65 per belt RRP from Ducati) and are claimed to be of equal if not better quality compared to OE. Stu at Exact UK offers great service too. Go to
www.exactuk.com to order.