As a beginner, a fast prime is going to be easier to learn to use, probably more fun, and a lot less frustrating than a speedlight. But once you've gotten ambient exposure down, and you've gone as far as fast primes can let you go, and you're looking for a way to move to the next level, you will eventually run across
the Strobist, and then you'll be happy you got an SB-600. But you'll probably be regretting you didn't save up for an SB-800 and/or D80/D90 instead. [grin].
Right now, I'd say go for the 35/1.8. It'll teach you the importance of max. aperture, DoF, and mastering your autofocus. But then, I'm enamored of fast primes.
