gping: Ping, but with a graph
I always liked gfblip: <a href="http://gfblip.appspot.com/" rel="nofollow">http://gfblip.appspot.com/</a><p>You can run this on your laptop and watch your WiFi drop in and out randomly (as other people around you download stuff, as Bluetooth devices interfere with it, etc.)  It's also fun to run a speed test in another tab, and watch the latency increase 10x as needless buffers fill up and your latency-sensitive packets wait in line so your router gets a better review!