I bought one from Amazon that transmits a wifi signal. I connect with my iphone and use an app that tracks an amazing amount of information. It works very well and cost less than $30 cdn.Now, after all this talk, mine also seems slow to heat up :--(
Time to get out the leftover-from-the-Prius OBD ... surely we have access to the coolant temp.
EDIT: I have an old ScanGuage II, does the job, but cumbersome to change readouts, etc. I've been waiting to get a dedicated Android and its associated app ... or something for my iPad mini, or the iPhone.