How can I output video from my HTC Thunderbolt to a TV?
The Thunderbolt has DLNA, so if your TV supports DLNA you can use that.  On my Samsung phone, you use the AllShare app for DLNA, but I think the Thunderbolt has another app built in.  Page 275 of the User Manual describes how to use DLNA.  This droidforums thread has a discussion of ways to use DLNA without a compliant TV, I'm not sure how well other ways will work.

There's also a "multimedia dock" that is supposed to be released shortly, it's "out of stock" until then.  That should provide a cable-based way of video output.