what do i need to buy, to be able to watch my videos from my thunderbolt to my tv.
If your TV missed the sudden DLNA upgrade of the past year, any client will do. Xbox 360, PS3, basically anything that can discover media available on the network and uses DLNA. Depending on what you use for a client, your media format choices might be limited. For example, an Xbox 360 can't handle 3gp video and it's unlikely that the TB can transcode. The HTC box they're going to put out will handle all the native formats of their mobiles. But Logitech's implementation of GoogleTV, the Revue, would be a good way to get DLNA plus much more and do it in the familiarity of Android.
To correct a post above, TB does not have an HDMI port. HTC is going the wireless route like Samsung.