The old Glacier Point Firefall is long gone, but every February and, as this picture shows, even in March, when conditions are right, Horestail Falls on El Capitan provide a nice natural firefall.
[update, 2011: Back when I took these photos — only back in 2007 — the Natural Firefall was getting popular already, but not like now. Only two years before that, the firefall would be in and you would be watching with 2-3 other people. By 2007, parking was already starting to be an issue. In the intervening years, it has gotten completely out of hand. People literally set up tripods in the middle of the road to get the shot! People have gotten stupid, parking has become impossible. For me, the event is mostly ruined by the crowds, sort of like the Yosemite Fall lunar spraybows, which now involve jostling with hundreds of people, including lots of people who don't know enough to turn off the flash on their point and shoot cameras, oblivious to the fact that they can't get an image that way. I have a pro photographer friend who, in the middle of a 60-second exposure has had someone come up with his headlamp on and ask what she was doing. Ridiculous.]