The Alfa AWUS36H 500mW adapter is the king of WiFi adapters, ask anyone who owns one. When you need long range wireless capabilities, you get the Alfa, end of discussion.
We have been developing a high powered 802.11n standard WiFi adapter called the N3, and physically it is beautiful. The adapter is being designed as a "functionality meets form" type of product that will bring long range wireless to Macs (it also works with Windows and Linux though) and do it in style. I got my hands on one today for the first time and was stunned, completely stunned by the results. At best I expected the adapter to work as good as our Rok500 wireless adapter, which gets great range but not quite as great as the Alfa AWUS036H. I was completely stunned when I hooked up the adapter and picked up several access points I had never seen before. I quickly verified the results using Wireless Monitor, and then hooked up an Alfa AWUS036H to compare. The N3 picked up 13 networks to 10 for the Alfa. I redid the tests and saved the results as images. The N3 also had better signal strength to access points in the same and next room, although the adapters seemed to receive about equally on APs further away. The N3 was not a great deal better than the Alfa, but it was still better, and that says a lot (these tests were done using the factory 2 dBi antennas in each box, as the Alfa 500mw has a higher max output power I am guessing with much higher gain antennas the Alfa would do better, but I will confirm that in later testing). Here are the images. In the next few days I will work to get a video test up here. Click on the image to see it in full size.