This question has been asked a fair few times now.
If its for windsurfing the majority of people here will recommend a Navi GT-31. A few will recommend a Garmin. I use a Navi GT-11 and its been working well for the last couple of years. There is plenty of support for the Navi. This is important when setting it up as its all a bit confusing at first.
I've covered makes and features in my GPS comparison:
www.mikeg.me.uk/guides/GPS_Devices_-_Speed_Sailing_-_Feature_Comparison.pdf
If you are buying a GPS predominantly for speed sailing then look closely at the GT-31.
OK, cool write-up.
What if I wanted a nuit that would do windsurfer speed and logs, but I also wanted to use for general navigation ?
I'm thinking ahead to my polar stuff here, for which I need to develop navigational proficiency as well as maybe bush mountain biking etc.