A lot can be done with a header of black and white. It would look good on a black background, as well as on a white one. For a more dramatic look, try using a black and white header on a blog which has a complimentary color as a background.
Have fun downloading this free header art. Try different ones on for size. Tweak them to your liking. Flip them. Resize them. And for special effects, try using a specialty font. Personally I like how metallic looks on black.
Use your imagination and let your blog reflect your personality.