As I've mentioned elsewhere on these forums, Handbrake is pretty good, and best of all, free. I personally use VisualHub at home and really like it. I use Sorenson Squeeze at work for professional work and it's definitely better, but for home use either of the first two are more than adequate.
I don't know of any software app that encodes to AVCHD. Honestly, I don't know why you'd want to do this anyway. Since your camcorder records directly in AVCHD, it makes for seamless transfer to Blu-ray discs, which is great if you plan to author in BD. At this point AVCHD is not well-supported by non-linear editors. It's going to take a while.