Purchased a VistaCNC Pendant the other day, so far, I am very happy with it, it seems to be very responsive, lots of nice features, and easy as it gets to install and get working. Just had to load the latest firmware in it, simple point and click, then copy the plugin files to the Mach plugin folder and restart Mach4, that's it.
Previous I was using a shuttlePro with some occasional odd behavior, i like this much better already,
http://www.vistacnc.com/