what is the default password for Airport Express?

There is no default password. None is needed unless you have configured one. If that's the case, and you don't know what it is, use a toothpick to push the reset button on the AEX while it's plugged into the wall outlet. Hold until the light starts to blink fast.

The AEX is accessed and configured using Airport Utility. It also came with a user manual.

Try your wifi-Password. Worked for me

The default password for the AirPorts is....

public

Reference this Apple Support Document

http://support.apple.com/kb/ht3728

Under what default settings will my base station.......

AirPort Base Station passwords are "public."

Bob, your response telling that user he "forgot doing this" was...kinda condescending.

You were wrong Bob. I just unboxed my brand new Airport express, launched the Airport config utility and clicked "upgrade firmware". Boom, it asks for password. Literally this has been out of the box for...2 minutes. I don't think I forgot setting a password.

In order to fix something, one must admit there is a problem. This is probably why 3 years after the original post this is still an issue.

public did not work because you previously setup a device password the first time that you configured the device. You likely do not remember doing this.

I can't believe I did the same thing. I was one step away from pin resetting it. Thanks so much!

Thank you so much!