This was instigated by someone (a person under the affects of a hallucinogenic drug, not an actual hostile person) losing control of his vehicle, swerving into oncoming traffic, and having a head-on collision while the PCs were standing on the sidewalk. The bulk of the session was done in non-combat initiative, as two PCs were badly injured by the car (which swerved onto the sidewalk after the first impact), and the remaining PCs tried to get their friends up, get the impact-bent car doors open, get the unconscious victims out of the cars, and drag everyone to safety before the small fires I was describing spread to the gas tank.
So it was combat, sort of, but with no combat or enemies per se. (This was d20 Modern, by the way. Sixth level characters, if I remember correctly.) I loved the tension. In retrospect, I wish I'd given more skill check opportunities to help players make use of their unique talents.
In the same campaign (a paranormal mystery game), I had crime scenes in which the PCs didn't have the opportunity to take 20 on checks because of things like an incoming rainstorm or a police squad that was going to kick them out. Trying to divide up tasks and hit different areas with skill checks in a short amount of time was almost as tactical as a mid-level combat -- "You, assist me! I'll take 10 here. Wallace, just grab the computer's hard drive -- we can always scan it later!"
I really enjoyed those sessions. More prep time than a combat-heavy game, in some ways, but really fun and different.