Jim Dunlop Original Cry Baby Wah pedal
This pedal does what it says on the tin. A forward click of pressure down on the pedal engages the wah and then you rock the pedal backwards and forwards to use the wah pedal which sweeps a filter up and down the sound to create the distinctive effect.
This is a hefty pedal, around 60cm long and 10cm wide. You aren't going to break this easily. The pot inside will give you many thousands of cycles before it needs replacing.
Does the job and no tone suck. Occasionally I find that with it engaged it adds a miniscule amount of hiss but that may well be the patch leads and not the pedal. (Update Sept 2011, I do find this pedal creates more hiss than hoped for, but I'm updating patch leads / power leads, so hope this will fix that!)
I'm not quite sure what the purists would think, but this pedal is great. Its nearest competitor is the Vox Wah pedal, but I simply purchased the Jim Dunlop as I needed for a couple of songs and my local store had the Jim Dunlop in stock.
I've used the pedal for funky versions of 'Lord I lift your name on high', for Mary Mary's 'Shackles' and a few other songs. Not used regularly so I tend to take this and don't put it on my pedalboard, but sit it in front of the pedal chain when I use it.
It is a passive pedal, so no power needed.