http://pixabay.com – Pixabay has tons of free images you can use without attribution.
http://www.3d-pack.com/#swf – 3D cover site
Unless you are a skilled graphics designer, keep it simple! It’s very easy to mess things up trying to get fancy.
Fonts: Title: Impact Subtitle – Times New Roman (serif font, better for smaller type)
Colors: Black and white. Again, don’t get fancy. It’s hard to mess things up using black and white.