Nelson Minar created this amazing map of the rivers in the contiguous 48 states. He notes on Flickr:
"I'm drawing all of the flowlines. This includes lots of seasonal creekbeds, arroyos, etc. That's why you see so much blue in dry areas. It also doesn't include places like the Everglades where specific flowlines haven't been defined. I may have bugs with a bit of missing data, too."
There's also a link to the GitHub project for the mapping where you can read the technical details and also find a super-high resolution (3840x2400) black and white version of the map above.