This post is an attempt to list and rank all the Rebellion abilities and combination of abilities that can cause wide spread destruction to enemy fleets.  This isn't meant to be a ranking of usefulness of these abilities/combos, but rather a listing and ranking of their potential power.

Tier 1 - Instant, Uncapped Destruction without Consequences

- The Maw + In-Gravity Well Jump - With a level 6 VL Titan, enter a gravity well, jump to a frigate fleet, engage Maw.  Not only does the fleet die within 5 seconds but you gain resources for each dead ship.  Its possible to wipe out over 1000+ fleet supply worth of frigates with this ability.  With the in-gravity well jump, the enemy fleet can't escape before you jump to them.  The only limitation is that this requires level 6 on a Titan that isn't very useful until it gets to level 6.

Once you get this ability, no group of enemy frigates is safe.  Even carriers can't escape this combo.  This is by far the most powerful frigate mass destruction ability in the game.  The Maw hungers...

Tier 2 - Instant, Uncapped Destruction

- Wail of the Sacrifice - For the loss of a Desert or Terran planet (or sometimes an Ice planet for weaker frigates) with full population, the Advent Rebels can use this ability to destroy (or causes massive damage) to all enemy frigates in all adjacent gravity wells.   Executes through a Temple of Communion at the planet being sacrificed.  Also causes moderate damage to enemy capital ships and enemy structures.

This ability spreads destruction over a very wide range and is devastating to enemy frigates but costs you a very valuable planet.  You can also use it in combination with Malice for even more destruction.

- Override Safety Protocol (Big Red Button) - TEC starbases, when upgraded with 2 levels of override safety protocol, can self-destruct and take out almost everything within a very large radius with them.  The upside is that enemy frigates and low level (or damaged) capital ships are destroyed.  The downside is that you lose the starbase and this ability also affects friendly units.

This ability is the most powerful mass destruction ability in the game in terms of what it can kill (did I mention that it takes out capital ships too?).  However, it doesn't have the range of Wail and doesn't provide resources like the Maw.

Tier 3 - Massive Destruction

- Chastic Burst + Malice - Fire up Malice on the Advent Mothership and then Chastic Burst on the AR Titan.  With high levels of each (level 3+), large numbers of frigate die.  Both abilities have to target the same set of ships and Chastic Burst has to be used before the Malice time limit expires.

This combo can be used multiple times within a battle to destroy huge numbers of enemy ships.  Depending on the situation, it may take more than one use of this combo before ships start dying.

Advent Note:  The Advent Rebels and Loyalists have a number of AOE abilities that can be combined with Malice.  It is possible to use multiples of these abilities to significantly increase the their total damage potential.  I.e.  Malice + Chastic Burst + Meteor Shower or Malice + Cleansing Brilliance + Scream, etc.  The key is to get the multiple abilities all to active within the 10 second Malice window.

- Cleaning Brilliance + Malice - Same idea as Chastic Burst + Malice.  As an Advent player, fire up Malice, fire Cleansing Brilliance at the same set of ships as Malice (targeting a ship in the back so that Cleansing Brilliance does more damage), and watch enemy ships go pop.  Timing is critical with this combo as Cleansing Brilliance takes time to line up and then charge up.

Cleansing Brilliance is a level 6 ability on the Radiance Battleship and has a long cooldown so you likely only get one shot at this combo.  However, if done right, it can take out a lot of enemy ships.

- Scattershot + Explosive Shot - Both of these abilities are on the TR Titan and both cause moderate AOE damage to enemy fleets.  When both are upgraded, the TR Titan can alternate between them causing massive levels of damage to a large number of ships over time.

- Missile Barrage - Use the level 6 ability on the Marza dreadnaught as TEC to target and kill large numbers of frigates at one time.  To use, move the Marza into the middle of the enemy fleet and active this ability.

This is a level 6 ability with a long cooldown.  It also has the disadvantage of spreading its massive damage out over a period of time giving the enemy a chance to run away / interrupt the barrage.

Tier 4 - Massive Destruction over Time

- Demolition Team + Boarding Party - The TEC Corsev Battlecruiser has the ability to blow up friendly ships in order to cause AOE damage to all surrounding enemies.  Damage is doubled if the blown up ship was originally taken from the enemy with Boarding Party.   The ability has good destruction potential when used multiple times in a battle.

- Fracture + Scream + Malice - The Advent can use this Malice combo much like Chastic Burst + Malice.  Fire up Malice, fire up Scream, cause destruction.  Add in Fracture before Scream for addition damage.  This combo has good damage potential when used multiple times in a battle.

- Nano Leach - VR Titan ability that drains hull points and antimatter from surrounding enemy frigates.  Slowly kills the frigates while healing the Titan and restoring its antimatter.  The real power in this ability is in making the Titan nearly indestructible when enemy frigates are close but it also does slowly kill large numbers of enemy frigates.

- Suppression + Subjugating Assault - This combo of abilities on the AL Titan effectively traps enemy frigates near the Titan and slowly "steals" them.  Not really an AOE that causes destruction, but this combo is very effect in dealing with moderate sized fleets of frigates.

- Meteor Shower - Ability of the Advent Starbase to cause AOE damage to all nearby enemy ships.  Can be quite deadly with multiple uses.

- Disruption Matrix - Ability on the TEC Loyalist Titan that does moderate damage to all surrounding ships.  Although it does some damage that can build up over multiple uses, its main purpose is to disable ability on all ships within its range.

- Volatile Nanites - Level 6 ability on the Kortul Devastator.  Increases damage to nearby enemy ships and causes then to each do a moderate amount of splash damage when they are destroyed.  Most effective against large numbers of relatively weak targets.

- Radiation Bomb - Ability on the Marza Dreadnaught that does damage to a single target and then a moderate amount of damage to all enemies near the original target for a short time.  Can be effective against tightly packed targets with multiple uses.

Please let me know if I have missed any AOE abilities or combos that can cause large scale destruction of enemy fleets or if I missed anything with how they are ranked.

Edit:  Moved Scattershot + Explosive Shot up to Tier 3.  (7/21/2012)

Edit 2:  Changed the names of the Tiers to more accurately reflect the potential for each ability/combo.  Added the ability to combo Wail of the Sacrifice with Malice.  Changed the wording on the Maw combo description to be more objective.  (7/21/2012)

Edit 3:  Added note on Advent Malice combos and added Disruption Matrix, Volatile Nanites, and Radiation Bomb to Tier 4.  (7/24/2012)