Here are some great rocket graphics resources:
Iconographics Design, specifically, their Rocket Shop section.
The Lycos Image Gallery, specifically, their Space section.
Xoom's Web Clip Empire, which you have to buy, but it's not to expensive.
Barry's Clip Art Server, specifically, his Space section.
Challenger Center, specifically, their Classroom Clipart section.
Mark Wade's Encyclopedia Astronautica, spefically, his Graphics section.
Jo'S World, spefically, her Space section.