http://bikeracing.ca/gabriola-youth-and-masters-omnium/
Three races over two days, cheap entry, and most interesting of all, the categories, A, B, C, and D, are determined by the first stage tt. So no having to race against superfast old/young/women/men who are in your regular category, but you really wish weren't there.
We use this format for the Axel Merckx youth weekend, and it results in very well matched racing in stage 2 and 3.