Google adds The super-trustworthy, anti-phishing key

Official Gmail Blog: New in Labs: The super-trustworthy, anti-phishing key: any email claiming to come from one of eBay's or PayPal's domains actually comes from them. We do that by looking at the "From" header, and when it says "ebay.com" for example, it means it really did come from ebay.com. Anything else is rejected; it won't even appear in your spam folder because Gmail won't accept it.

Turn on "Authentication icon for verified senders" from the Labs tab under Settings, and you'll see a key icon next to verified emails that are super-trustworthy.