PortaPaddle from American Morse
The PortaPaddle seemed to be the most popular. These keys come in a kit and can be deployed in many different ways. They seem to be popular anchored to the top of a RockMite rig
Te Ne Ke
The Te Ne Ke also received several endorsments. This key is very light and can used in a varied of ways. You can actually hold it in you hand with the paddles pointing away from or you can order it with a base that holds the key pretty firmly.
This key comes is a key and takes some soldering, but is very compact if built into the rig you are using.