Forgot email associated with my itunes account
You could have a look in your keychain.

/Applications/Utilities/Keychain Access.app

Select the Login keychain in the top left panel and the All items in the bottom one.
Use the search in the top right corner.
Search for iCloud, MobileMe ,iMessage or Apple ID.

Double click any of the items that come up and see if the jog you memory.
Most of these will bring up the email for your apple id.