What keyboard testing utility do you recommend?

[EscapeVelocity]

Thanks. Gonna test some of my vintage keyboards.

[E TwentyNine]

Aqua's

https://geekhack.org/index.php?topic=34670.0

https://geekhack.org/index.php?topic=6643.0

[EscapeVelocity]

Thanks mate!  Just what I needed!

[False_Dmitry_II]

Definitely. I still haven't seen one that even compares.

[Melvang]

I use elite keyboards program called Switch hitter.  The nice thing about this program, is it can alert you to bouncing keys.

[Blaise170]

It's not exactly a "test" program, but I use WhatPulse.

[Snowdog993]

I use this:
http://www.softpedia.com/get/System/System-Info/Keyboard-Test-Utility.shtml

[EscapeVelocity]

Thanks for all the recommendations so far...

[chyros]

I use Switch Hitter, but I'll check out this Aqua thing too. 

[phoenix1234]

I used both AquaKeyTest and Switch Hitter.
AquaKeyTest can be standalone application and Switch Hitter required a installation.
Both of them are general good and light weight.
If I must choose only one, I will choose Switch Hitter because it can detect the key chattering problem which is likely happening with mechanical keyboard.

[chyros]

Just tried Aqua; it's not too special tbh. I'd say Switch Hitter is better; allows for different layouts, higher contrast and colour customisation and chatter detection, none of which Aqua has.

[davkol]

Microsoft's web applet… it works only for some keys, but runs in any modern mainstream browser.

Otherwise, I use showkey.