I forgot that Keychain has a simple feature which will show you any password you've stored in it.
This past New Year's Eve, I was at the childhood home of a high school friend where I was showing him, his mother, and girlfriend how to stream photos, music, and video to their Apple TV from their computers, iPhones, and iPads.
When it came time for my friend's mother to enter the password for her iTunes account she had forgotten it. In the blink of an eye, she opened the Mac's Keychain app, which is in the Applications/Utilities folder. "Go Mrs. G!," I thought to myself. I suspect that she learned this trick from her brother who's worked at the Apple Store on Fifth Avenue. And a valuable trick it is.
1. Once you've opened Keychain, click on the username of the account that you used to login (jmoreno in the above screenshot).
2. Click on Passwords category, since it's a password that you want to recover. You'll have to find the MobileMe, iCloud, iTunes, etc account that you're looking for under the Name column (also, you can enter the account name, i.e. iTunes, Mail, etc, in the search box, in the upper right to narrow down the search).
3. Click on the Show Password checkbox. Keychain will ask you to enter your Mac's account password. The password that you're now entering is the one that you use when running a software update or after rebooting. (You need to enter your Mac's account password since it's used to decrypt the password that you're looking for.) Once you've enter your computer's password the password will be displayed "in the clear."