This might not count because a) he's a dude, b) it's been ages and c) he's not a natural blonde, but...
Ben Reilly was a brown-eyed blonde. In fact, blue eyes in general seem to be pretty rare. Spider-Man's the only brown-eyed superhero I can think of off the top of my head. And even that varies depending on the artist (or medium, with Tobey's blues).