I like my planet bike computers. One has a thermometer, and the other doesn't. The thermometer isn't exactly accurate - it runs four degrees cold in the winter and hops around a lot when it's warm. I love how it resorts to the clock in the corner as a default on my commuting bikes where time matters a whole lot more than average
They're not hard to install... tho' I stopped with putting one on the Dahon because I couldn't figure out where to send the wire so it would be least likely to mess up in the folding process. (It's 'way too long from wheel to handlebars for wireless.)