been using a couple of the $10 Schwinn units from Walmart for a year through the winter and rain and stuff. they provide:

distance
max speed
avrg speed
elapsed time
current time

I clear it out after each ride so that I have the STATs for every ride. kind of annoying - there should be a button for "clear trip" or something like that

http://www.viewpoints.com/Schwinn-12...r-review-50f75
http://www.rickshawseason.com/tag/cycle-computer/
http://www.youtube.com/watch?v=ifKlfpSeYA4

it was easy to install once I understood the basic concept: little magnet gets screwed to spoke which passes skinny sensor zip tied to fork where wwire gets wound around a brake cable up to the bars where you zip tie the bracket for the computer. the computer slides on/off the bracket.