GMAIL New feature
For all of those forwarding their other accounts to gmail and just replying with GMAIL, now you can verify an address other than your gmail address and then send as that from gmail.
Just go to your settings and the accounts tab to "Add another email address".
This will bring up the option to verify the address with a link in an email to that address which you click and then you have the ability to email from it.
Now you can get the free spam filtering and great mail functionalities of Gmail with your other email accounts too.