I haven't done a thorough enough search, perhaps these have been discussed...
Capabilities:
Smoke grenades... More a capability than a flag. Real tanks use white phosphorus smoke charges to instantly cloak themsleves against an incoming optically guided missle. Wouldn't really work for laser (no reaction time) but would essentially CL you against other attacks, esecially GM.
What about player-selectable cannon dynamics... player can opt for longer range with longer reload time, increased shot count but shorter range, etc... Player can select the gun mode for the given situation, each with a balanced tradeoff.
Flags:
Smoke generator flag... allows a tank to drive along and lay a temporary, linear CL smoke screen, that teammates (and enemies, of course) can drive behind.
"Laser grips" flag... regular, default cannon... but a red bore line displayed on the radar display out to the max weapon range.
Mortar flag - fires in a high arc over obstacles-- maybe even an aiming dot on the radar, which is offset by longer flight times... maybe has a small "SW-like" burst radius on impact?
Engineer flag- allows you to place obstacles (like digging tank ditches) that impede movement
Offensive Counter-measure Flags: (flags adversely affect, but don't kill target)
Stingray flag- momentarily blinds enemy out the window or on radar (There is an incapacitating laser in military service called "stingray")
Malathion Flag- a non-lethal flag, that if I hit you, you don't die, you are a temporary "carrier" and you kill your own teammates if you get to close to them.
Teleport Flag- you teleport the tank you hit to somewhere else
Taser- stuns/disables, but does not kill an enemy
Just thinkin out loud