Differences between the HG20 and HG21

There's a single instruction manual for the HG20 and HG21. In a few places, it calls out differences between them. I'll list the ones I find here.

Hard Drive
The HG21 has a hard drive that's twice as large as the HG20. As I mentioned in another post, you can record up to five and a half hours of high definition video on the HG20's hard drive. You can store twice that, or about eleven hours, on the HG21.

Viewfinder
The HG21 has a viewfinder you can look through rather than relying on the LCD screen. Since I always use the LCD screen, the lack of a viewfinder on the HG20 didn't bother me. The viewfinder could be useful in very bright conditions that make the LCD hard to see.