I was browsing some Japanese blog of a player I know, and there were a couple links to interesting programs that I had not heard of before.
First, Flash-based tests meant to measure your average reaction time to visual stimulus:
http://70.84.61.34/~fundotn/Games-D5-140406/reaction.swf (can be used offline);
http://www.humanbenchmark.com/tests/reactiontime/index.php (online with leaderboards).
I have an average of 175 ms on those two tests.
The second is a Windows-only
ABX (blind test) program that measures your sensitivity to input lag. When you start, you need to choose the test variable. "1 or 8" means one subject will have 1-frame latency and the other 8-frame. You can switch between them using spacebar. When you determine the lagged subject, press enter to write down your choice. Repeat until 20 results.
So far I've managed to pass 1 or 3 test with 100% confidence, but in 1 or 2 I can only guess.
Disclaimer: I'm using a CRT monitor, USB mouse and PS/2 keyboard.