Fun with turrets
You can pick them up, toss them around, make them fall indefinitely through two portals, drop a cube on them, etc. Also try the following: use the incandescent particle field in front of the exit. The computer voice said before that all objects other than yourself and the portal gun will be destroyed. Pick up a turret and toss it into the energy field. The turret will say "ayayayay" as if being electrocuted and disintegrate.