The drivers side window wasn't winding all the way down, and every indication was that it was getting caught on something.
So when I finally had the time, I pulled the door trim off and had a look. As suspected, the bottom edge of the glass was catching on a cable that had come loose.
Once I had that cable re-secured, the window was able to move freely again. Most annoying thing was that I didn't take a phot while the door trim was off. D'Oh!