Due to a API update with weather.com awhile back, all old xfce4 weather plugins stopped working.

Here is a list of proposed updates that should fix the API errors. Note it may be buggy.
Direct Download DEB's

Oneiric 11.10: i386 amd64
Natty 11.04: i386 amd64
Maverick 10.10: i386 amd64
Lucid 10.04: i386 amd64