I tried to compile information on how to hard reset most Windows Mobile phones. If I am missing any device please let me know using the contact form on this blog. I will keep this updates with new phones as they become available.
Touch - Hard reset is done by holding the green and red buttons and then pressing the small button beside the USB plug
Motorola Q9c - Power on holding the center button and it will ask you if you want to hard reset..
Mogul – Hold soft keys while pressing reset button on the side
Motorola Q - Power on holding the center button and it will ask you if you want to hard reset.
Motorola Q9M - Power on holding the center button and it will ask you if you want to hard reset.
Blackjack - Just power on holding up on the DPad and it will ask if you want to erase all data. Press 1 to erase and y to confirm
Cingular 3125 – Go to Accessories in the Start menu and select Clear Storage. If you can’t access the menu turn off the phone, and hold both soft keys while powering on.
Motorola Q9 Global - Turn on the phone while holding the E and Z keys.
AT&T Tilt - While holding down the two soft buttons on the front of the phone (above the Windows and OK buttons) press the reset button with the stylus for a second.
Palm Treo 750 – While holding the red “end-call” button press the soft reset button next to the mini-SD card slot for a second or two.
Cingular 8125 – While holding down the two buttons on the side of the phone (top right and top left – Comms and Voice) press the reset button with the stylus for a second.
Dash – Turn off the phone. While holding both soft keys press the power button and hold for about two seconds, then let it go. When the confirmation message comes up you can release the soft buttons.
Wing – Hold both soft keys while pressing the rest button on the side of the phone.
Shadow – I guess you could hold both soft keys and press the rest button
HTC Devices - Fot most HTC phones hold both soft keys while pressing ghe reset button or powering up
HP iPAQ 910 - Press and hold the voice recorder button (on the left side) and the OK button (on the right side) simultaneously, then press the Power button. Hold all three buttons until you see the Clean Boot screen.
HTC Diamond - With the phone on, hold volume down and the round key, then press the soft reset button on the back of the phone. A message will appear asking to press volume up to do a hard reset.
Many phones have a "Clear Storage" or some other master reset application in the Accessories folder under Start menu
Thanks to gekko and Matt for the comments.