Re: portable GPS for measuring speed
I don't have any experience with other brands, as the only GPS that I've used is an old model from Cobra (yup, the radar detector people). I bought a used GPS-1000 from Ebay about 5yrs ago for only $60. Its pretty big compared to other units, and the screen is only grayscale. What I like about it is that you can go screen to screen very easily to access the different modes. There is also a screen that you can setup multiple parameters on (speed, elevation, etc). When I go dirtbiking, this is the screen that is almost always used. You can set it up with either 3, 6, or 12 different parameters being displayed at the same time. The screen and buttons are large enought that I can use the GPS while riding down the trail. I don't have to stop to fiddle with it. They are water resistant, back-lit, run off batteries or 12v cig lighter adapter, have roadmaps, and may come with mounting options. Mine came with a really handy suction mount for windshields.
Here is a shot: