Over on the Official Gmail Blog, Google's Sri Harsha Somanchi lets us know that Gmail now offers the ability to "block" unwanted senders. Sri explains that after you block someone, any further mail from them will go to the spam folder. He also explains that the new "block" functionality and the current "unsubscribe" functionality are coming to the Gmail application on Android.
If you're wondering how to later unblock a sender, Google has published a new Gmail Help page explaining this and more.
(For more detail, Chad White from Litmus has blogged about this in more detail here.)