To make a very full pom-pom: Cut 2 donut shapes of cardboard, wrap with different colors of yarn (or make it all one color) cut the yarn on the edge between the 2 pieces of cardboard, wrap a piece of yarn in the groove and tie a knot as tight as you can. Remove the cardboard and fluff.
Awhile back Ivy attended a friend's tutorial on making pom-poms. I kind of wondered at a tutorial for that and what you would do with pom-poms other than decorating knit wear (this wasn't a knitting circle thing). This is a pretty great idea. Also, a good way to use crappy yarn that all knitters and crocheters seem to accumulate from thrift stores yet never really want to knit with.