I had a set of formulas for calculating the RMS value of many different wave forms i'll have to look for them, but im sure there is much on the web too.
One thing i always meant to do was to measure the RMS values of current and voltage in rectifier diodes where there is significant capacitive filtering that makes the current wave shape almost like that of a pulse. I have plenty of spice data and even a special program for calculating these things, but it would be nice to have some real life measurements.
I got my first AC+DC meter about 2 years ago even though i have used them before. I should break it out and do some small experiments with low power supplies like 12v, 1 amp or something like that to start.
Have too many other things going right now though.