What are my options?

I realize that's the primary spot for a dyno powered light, but unsure of what format my next rig will run- 20", 26", 700c, or 29er- so not willing to invest in a dynohub yet.

I use a Cateye HL-EL530. I wish I could say I recommend it but alas, I cannot. It's okay, just underwhelming. I do like the fact that it's self-contained and runs on 4 AA batteries. I also like that it only has one steady "on" setting (I have a backup blinkie). It does help me to define potholes, but it's output is less than impressive.

I mounted it to my fork crown using an Ixon Speed fork crown mount (scroll down the linked page to see it) that I got from Peter White Cycles. He offers a lot of different battery-powered lights that are a step above the 530. In fact, he has this to say about the 530:

I guess I should have done my homework a little better. If I were to buy another battery-powered headlight it would be the Busch & Müller Ixon IQ Speed.