Did you know that TV Tropes has a dedicated recommendation page for Dr. Who fan fiction? Now you do, and so do I. It’s where I came across this gem of story, a Doctor Who/Firefly cross-over. I found the ending a bit weak, but the first half that describes the crew’s reaction to a fast-talking, hyperactive David Tennant is brilliant. And the opening chapter gave me actual goosebumps:
River was sitting up straight in her chair, hands motionless on the console, eyes staring wide into the black. […] She turned to look directly at him. Her eyes were black, the pupils were opened so wide. “The storm. It’s coming.”
Go read it, it’s worth your time.