Velocitek's products are nice- look at the online store here to see. They are kind of pricey but are made specifically for sailing and combine other functions (start timer, shift indicator, etc.). Other options- if you have an iPhone there are several cheap GPS programs, but get a GOOD waterproof case! There are even some specific for sailing- I like GPS MotionX but I only use on my relatively dry keelboat. Another option is the Fortrex wristwatch style GPS units sold primarily for running/biking but work on the boats as well and I have used one of those as well. You can get them pretty cheap on E-bay- battery life is limited though.

Hope this helped!
Kirt