There are so many free ones in Market ... It's really a matter of which one suits your needs. Just do a search for "WEATHER" in Market and try a few until you find the one you like. Personally I use Beautiful Widgets - but it costs like 99 cents or something. It includes a nice set of different Weather Widgets.
I personally like Fancy Widget on the Market. They have so many different clocks there it's unreal. Plus, I can put my clock and weather together! I hope this helps. I have the LG Revolution and there is a picture of mine with the app on.