That's hard to pick just one. I think the band saw is very valuable, but so is the belt sander, and I guess if I didn't have the belt sander I could just get by with drum sanders for the drill press? Man, I sure use that belt sander for all kinds of stuff, not just bow building but lots of projects. Drum sanders are cheap though, if you have a drill press it comes in real handy for getting close to your lines when your trying to rough in your limb profile.
I've already got a dust collector cause my father is a wood worker.