KISS is a really good thing to keep in mind for situations like this (Keep it simple</b>, stupid.) Subtlety in your patterns (if you're using them), readable fonts, and colors that don't clash; images that lend but don't overbear (again, if you're using them.)
Places like Subtle Patterns are good for if you want to keep the award design simple and clean. This guide of mine is more for making layouts, but some of it may help.
As ~crazyquilt mentioned, dA does have some good stock, but make sure it's categorized as stock, because some artists may not be too happy about their non-stock art being used.
As for layering text over images, outlining the text or using a shadow effect is always a good, simple way to go if you need your text to pop more.
Or, you could always go the route of making each award banner character-specific, and use the PB's image for the banner. It's more effort, but it's a lot more personalized. Not for a game, but here are some banners a friend and I did last year for a fic contest on a comm I run.