u definatley want a spare battery... i normally use 1 and a half batteries during a night of photography. What really chews your battery time is long exposures!!
will also need a cable release.
I am using only the stock standard lenses at the moment.
I'd probably go for a 1 gig CF card too. that way u wont run out of space ..specially if your taking images in RAW, and if your at a astro camp then u won't need to upload or change CF cards half way through the night!!
ohh and the price seems good too!