I have Orinoco cards and I bought an antenna from lucent like this one:
Its good for 3db, and I picked up about 20-30 more foot range on it. Its not outdoor tho. I have it just inside the truck and pull it outside onto the roof when im in the driveway if I need extra distance.
I use an airport as the access point, so I'd like to get another one of those for the access point
mosta these antennas are expensive. I got mine on ebay for 40 bucks tho