AVCHD (Advanced Video Codec High Definition)
This format is used for several HD. The Sony SR10, SR11, SR12. Canon HG10.
The Sony cameras ship with Sony Vegas Pro 8.0a, but it runs under Windows.
According to this posting, the nightly build version 0.9.0-test2 of VLC will "decodes those files without too many issues".
According to this page, FFDShow will also play/decode the files.
Transcoding MTS/M2TS AVCHD Video Files with Free Software Good tutorial.
Another Tutorial (This includes installing software in a non-Ubuntu fashion)
According to above Wikipedia article, ffdshow tryouts is an Open Source player
I've written some up to date instructions for converting AVCHD to MP4. It's much simpler on modern systems (Ubuntu Precise in my case).