We have a small DC clamp-on ammeter, similar to this one
http://www.kmstools.com/darson-instr...amp-meter-1868 that comes in really handy for monitoring how our motors are working. If you're running Jags with serial communications, and you want to write some code to monitor current consumption then you probably don't need one of these. But if you just want to quickly monitor how much current draw a motor is pulling, then just clamp one of these over the line and read it.
Just make sure you get one that reads DC current, and you really don't need one of the ones that measure up to 400A. The lower maximum values often offer higher resolution.
Jason