Quick LED torch (or flashlight, if you prefer):

From the lock screen, swipe UP for the camera, then turn on the video recorder, then turn on the LED flash. I don’t know about you but I keep that stupid flashlight (torch) app in a folder on my third page of apps, and the one I’ve got takes a stupid long time to load, so 1 button press, 1 swipe & three taps is pretty darn quick. You may also account for even more time to unlock the screen if you’re the kind of person who always keeps your iPhone locked. 

Also, once you’ve turn the video recorder on it will remember that setting for the next time until you turn it off, so you’ll have to flip it back to still mode if you want to take a photo next time you swipe up for the camera. Taking a few random videos may be a small price to pay for a little less time fumbling around with your phone in the dark like a buffoon.

(ed. note: I forgot to mention that swiping UP on works in iOS 5.1, but if you’re running 5.0 you can double-tap home and then tap the phone button. But if you’re like me you sometimes experienced an awful long wait for the camera app to open up unless you were already running it before you locked your phone. Maybe this will give you a good reason to upgrade? Also, on an unrelated note I’ve noticed a decent improvement in battery life with 5.1.)