Ratchet and Clank. Combine it with the rift-ripper from Ratchet and Clank 3. Alternatively, anything with an escort quest, just shoot a portal at the start, make the person wait, get to the end, 'Portal!'. Mission Accomplished.
EDIT: What I'd really like would be the ability to shoot portals through other portals (not in portal, that'd be cheap, but in other games) you could, in most cases, traverse a entire maze only going through a portal once.
EDIT: Actually, imagine a passive-aggressive shooter, where you didn't kill people, but used portal guns, or boost-pad launchers, or air-tunnels etc, and you had to warp/boost/air-push/etc people off edges or from rooftops, or onto the bottom of a lake to kill them.