(this is not a sponsored recommondation!)
My friend's mobile phone came with some pretty cool guitar software - a pitch pipe, a chord dictionary, and a metronome - and I wondered if any of these could be downloaded free online. After searching and trying out various programs, I found that this was the best - it had all three functions within a single program, not bad at all!
Check it out at: http://www.chordmaestro.com/
Here's a screenshot, see the website for more: