Finally Canon has suppled a their own Filter Adapter for Canon SX10, SX20 and SX30 Cameras. It's called Canon FA-DC67A Filter Adapter. This Canon FA-DC67A Filter Adapter is perfect for Canon SX10 or SX20 or SX30 Cameras. It's well built and solid. The FA-DC67A Filter Adapter is designed to move along with the lens while zooming, preventing vignetting at the wide-angle end of the zoom and providing filter coverage throughout the full optical zoom range of the lens.
Downside of this Canon FA-DC67A Filter Adapter is You can only mount 67mm Filters. Which are expensive than 58mm Filters which you can mount with usual Janco 58mm Filter Adapter. Also the price difference between Janco 58mm Filter Adapter and FA-DC67A Filter Adapter. Janco Filter Adapter is only $9 at Amazon.com and FA-DC67A Filter Adapter is around $39.