Update - these sites no longer work so dead links have been removed.
Sterling Udell, creator of the DayLightMap Google Maps tool (which lets you see a world day/night view of the earth) has added a VERY cool new feature.. "Near Real-time" NASA cloud imagery! Take a look:
The images are obtained from NASA and are up to date within the last 6 hours. You can also take a look at the timestamp for the cloud imagery! Pretty nifty! :) Sterling has more info about the imagery on the left side of the page. Be sure to also check out his really amazing "World city lights at night" map which shows a satellite image of the world's city lights taken from space!