Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.
I've been using FSrealWX lite and have been really happy with it. Available from this web site: http://www.rs-transline.de/index.php?page=self&id=2
The author, Silvio Lafere, is very prompt and helpful in responding to support requests.
Al
edit - looks mjrhealth beat me to it while I was typing, great program, well worth a try
Where can I find FS Skyworld 2004?2- FS Skyworld 2004: REX little brother for FS9, but once again the clouds (and ONLY the clouds) are compatible with FSX. The textures are in lower resolution (512) but you get a LOT of choices, with a graphical interface. Some of those clouds look really good, and they are quite FPS friendly.
There not, (if memory services me correctly) they were pirated REX.FSRealWX.
Clouds, etc...
http://www.sim-outhouse.com/sohforums/showthread.php?28684-New-freeware-FSX-environment-files...
Don't know if they're still available though.

I've been using FSrealWX lite and have been really happy with it. Available from this web site: http://www.rs-transline.de/index.php?page=self&id=2