One thing to keep in mind, although it is only my opinion, your numbers' stying should match the degree of "radness":biggrin: of the rest of your ski, otherwise they will really stand out like a sore thumb. If you don't have super-duper rad graphics overall and you have only straight lines on the paint/decals, I wouldn't suggest going with tribal reg numbers (for example).
I was pretty happy with custom made vinyl (silver metallic) block reg numbers with a 20-30 degree tilt to them to give them a little "radness."