It’s hard to find good, fast and cheap prime lenses and it is even harder to find zoom lenses! The Canon 25-100mm f/1.8 is one of the few cheap and fast zoom lenses. You can find some image samples at 406club.dyndns.org. They used the Panasonic G1 to take the pictures.
Advent (DVXuser forum user) tested that lens on Micro Four Thirds cameras and said that it is “extremely fast zooming and very sharp”
A cameraporn pictures can be found here at getdpi (Canon 25-100mm on the GH1).
The lens is available at eBay (Click here to see current auctions and price).
P.S.: A high-quality alternative is the Olympus 35-100mm f/2.0 Zuiko Lens for E Series DSLR Cameras but it is 10 times more expensive.