From a post on /r/Arduino I had some ideas about how to make a simple wind sensor.
Tested one of the Hall sensors I have with a neodymium magnet I took out of an old CD-ROM. The particular Hall sensor in the breakout board is a 49E501BG. At first I tried another Hall sensor but the output from that one was almost digital, useless.
When I tested it I attached the magnet to the tip of a screwdriver and moved it around in all kinds of ways around the sensor. It gave nice clear readings from 300 with the magnet at its closest to 600 with no magnet or even 800 if the reverse side of the magnet was close.
Pingpong ball would give the wind more to drag on. A dampener (more rubber bands) would be good so that the magnet doesnt move too far away even in a full storm.