From Lifehacker.com, a great article on Extensions We'd Like to Go Mainstream:

"Like TV? The TV Manager extension lets you browse listings and set alarms for your favorite programs from the comfort of your browser. The extension supports most US channels and is completely customizable. If you set an alarm on a show, TV Manager displays a simple reminder when the show is about to start (perfect for ending your Wikipedia run before you miss your show)."

Read more: Lifehacker.com