I would have to agree that a Star Destroyer vs. the Battlestar Galactica would be an awesome fight, but my money would be on the Star Destroyer. Star Destroyers have planetary strength deflector shields, in addition to the 60+ turbo laser emplacements, and concussion missiles, and stormtroopers, and assault blastboats. Of course, if the Galactica manages to get a lucky shot off with one of its main forward lasers, then that might be a different story.
I always wanted to see a Star Destroyer vs. the Defiant from DS9. I think the Defiant would tear a Star Destroyer to shreds in no time flat!
Respectfully,
Martok2112