We, for the first time, have a (5' artificial) tree. We've made salt dough ornaments and it looks homey, if a bit amateur (which is how i like my trees). Problem is... no topper. A salt dough topper would be too heavy, methinks. I'd like to stick with homemade because there's nothing nice available in the stores here. I knit, and thought about a felted angel or star, but don't have any yellow or white felt-able yarn. No local yarn or craft store, so we're talking common household products here.
Simple: a Santa hat... or any small knit hat
A little time/effort: construct a start out of twigs or small tree limbs... you could use twine, pipe cleaners, glue, wire, yarn, or twist ties to hold it together. Weave in a few branches with berries, or wrap the star with multi-colored yarn. This would be a very sweet, homey tree topper!
Ooh, I like the hat idea. Not too many trees around here to gather branches from, but the hat could be cute :D.