In 2010 I saw this great device called Teradek 220 that could stream full HD video wireless. At the time I felt this to be exciting because during a shoot clients and producers could use their laptops to display what comes out of the camera.

More than a year later I got hold of one unit from the first batch of these streaming devices - a
Teradek 220. Since it's older hardware inside you can't run the latest firmware but it does provide for both wireless and ethernet streaming, a feature not on the current 220 unit. Then you'd have to go for the
Teradek 250 which will give you better wifi streaming at the same time as ethernet streaming

It's a small unit that mounts like shown here on the cold shoe on top of a camera. You plug in HDMI and power (7-24) and use your laptop to view. In theory it sounds simple enough.
If you choose to stream via wifi the stream is very sensitive to interfering signals and will drop out pretty quick. The bandwidth becomes to narrow when using more than one viewing laptop so it sounds good but in reality isn't the best solution.

A better way to use the
Teradek 220 is to hook it up to a wireless router and stream from the router to more than one laptop. You can use an iPad if that's your game. The streaming server inside creates a stream which is viewed in VLC or any other program that can read the rstp.
If you go all ethernet it's rock solid streaming and it streams both video and audio from the HDMI connector. It codes incoming video to H264 so quality is good.
You have many options inside which you adjust through a connected PC and can stream from 480 to 1080 with many different frame rates and bitrates. You can even adjust delay which influence how much lag there is. A low setting results in a short delay but at the same time doesn't provide as much buffering as you might need. A value of about 250ms is recommended so you'll end up with 1/4s delay. Not ideal if you look at the actor at the same time as the screen and especially with regards to audio delay. But if you've parked your client in another room or further away from the set it's a very useful tool.
I haven't got the chance to use it at a big shoot yet but I will as soon as I can.