This is probably obvious but what the hell...
Materials: good, safe, spray-on lubricant--ideally with a straw-spout attachment (teflon or silicon are probably safest -- I've used WD40 but this may prove to be damaging in the long run).

Step 1: roll down windows most of the way.
Step 2: spray lubricant of choice into rubber rails/guides in the door frame (you know, the parts where the side edges of the windows slide).
Step 3: roll window up & down to spread lubricant.
Step 4: enjoy smooth, quiet window operation.
Step 5: repeat lube process as necessary

I've done this twice in the past year; usually a heat wave causes the windows to go bad then I lube & forget for the rest of the summer or so.
When I first noticed my window problem, I tore apart the door panel & did all kinds of inspecting & concluded...the power window mechanism is simply a bad design. The window is propelled up & down by a metal/plastic assembly located at the bottom/center edge of the window & guided by rubber rails on the sides (there is also a center rail, of course). The center guiding assembly has lots of play/slop in the components so the grabbing of the side rubber rails causes all kinds of pitch, roll, and yaw in the mechanism wich leads to component binding & consequently window movement slowdown. With the rubber sliding rails lubricated, they can't "grab" nearly as much & the window operates much smoother.

As you said, kinda obvious, but a helpful post nonetheless...thanks!