MPEG Streamclip is decent for OS X for being nearly free. (needs the Apple MPEG-2 component).

Sadly I still don't have an easy way of editing commercials from my ReplayTV MPEG2 files and burning them to DVD. Every way I try seems to enjoy retranscoding the files for no reason, usually into DV then back to MPEG 2. This leads to some horrible results since the source is interlaced to start with, but gets re-encoded progressive with no attempt to deinterlace.