For those looking for an outdoor antenna for their scanners, you can try an omni-directional VHF Amatuer Radio antenna. The ham band is from 144 - 148MHz, so it's not an exact match, but it will work just great for recieving and can be found for very affordable prices. Radio Shack also makes a discone antenna that covers DC to light...a bit more expensive, but a good antenna. If your scanner has a BNC antenna connector on it for the "rubber duck" that came with it, all you'll need to do is get an adaptor for the PL259 connector on the ham antenna (also cheap and available at most any electronics parts place)
antennas tend to be directional yagis. They will work, but the ham antenna is more practical and (probably) cheaper.
Whatever you go with, get it as high off the ground as possible!!
Hope this helps,
I see my Cats as Companions. My Cats see Me as Furniture!