Have long thought about building a dynamic balancer. Very useful for crankshafts and blower rotors. Easy enough to build a very simple balancer and nowadays not too much more difficult to build an accurate one. Electronic controllers are very accessible, as are the necessary transducers.

Balancing a VW crank is pretty straightforwards as it can be done without bob-weights so the only thing that needs to be measured is the vibration amplitude and angular location. On a basic machine you can get away with just the angular location and then use trial and error to determine the weight needed. Here's one such machine that simply uses contact points and a strobe

https://www.youtube.com/watch?v=ZbmozBlYylw

If you want to get tricky you can add accelerometers to measure the amplitude and then use a spreadsheet or software convert this into weight.

https://www.youtube.com/watch?v=xP_Fc8actok

https://www.youtube.com/watch?v=m4mfHe8Nzm0

Here's a lik to an excel spreadsheet written by Conrad Hoffman - http://www.conradhoffman.com/CRH01.htm There's a bunch of other good stuff there too

Balancing.xls (26kb)

Theres also an iPhone vibration analysis app that could be used.

http://www.instructables.com/id/Dynamic-Motor-Balancing-with-Sugru-and-an-iPhone/