From Going Apps:
We have just up-graded the Wind Meter APP so that it now works for both 3G and 3GS iPhones. Also included is a new movement feature. The Wind Meter APP has been in the top 20 Weather Apps at iTunes now for 6 months straight!
Wind Meter: use your iPhone to measure wind speed. Wind Meter works by measuring the volume of the wind on your iPhone microphone and converts it into a wind speed reading. To use, simply point the microphone into the wind and push Get Wind! Wait a few seconds and push Got Wind! The final reading is the average of the period. Wind Meter supports multiple units of measure including Miles Per Hour, Knots, Kilometers Per Hour, Beaufort, and soon Feet Per Second, and Meters Per Second.
Use Wind Meter to determine the wind velocity for a variety of recreational uses such as (but not limited to): windsurfing, kitesurfing, sailing, rc flying, hang gliding, golfing, hunting, fishing, rowing biking, tennis, and many more.