Thanks everyone for all the suggestions. MODIS is a high-res system
but it is only good for analysis the next day.
Probably the one that best fits my vision of what I wanted is the one
from Bob Gibbons.

For other regions, see;
http://wxcaster.com/vis_overlays.htm

Bob

This has the folksy name of "Earl's 1km Visible Satellite Image
Overlays" and has a simple menu choice.
I plan to use it for last-minute XC planning when deciding which
direction might have a nice area of cumulus.