Do you mean for your phone, or for AndroidForums?
Assuming you mean the phone, all I can suggest is checking your other email account(s). You should have received a "welcome to GMail" type mail when you created it. Or go to GMail on the web, go to the login page, and tell it you are having problems logging in, and that the problem is that you've forgotten your userid. As long as you can guess what your recovery email or phone number is, it can send you the address. Then you can reset your password. May not help get into the device, unless you still have an internet connection on it, but at the worst you'll at least be able to reload your paid apps if you have to do a factory reset.
Our general advice for being locked out of the phone is here: http://androidforums.com/faqs/685025-lost-phone-locked-out-faq.html
If it's your AF account you've forgotten, my best guess would be to contact email@example.com
(site administrator). If you know what email address you used when you registered he should be able to find what your login details are.