In Space:
Phaser: Chance to disable a random subsystem
Disruptor: Chance to debuff damage resistance
Plasma: Chance to proc a fire based DoT
Tetryon: Chance to proc Shield damage
Polaron: Chance to drain power from all subsystems
Anti-Proton: Bonus Crit damage
Projectile:
Photon: Less damage but faster fire rate. Regular boff effect.
Quantum: More damage but slow fire rate. Regular boff effect.
Plasma: medium damage with a chance to apply a DoT that ignores shields (decent against both unshielded and shielded targets). Plasma's version of High Yield fires a Plasma Ball that can be targeted and shot down.
Transphasic: low damage, but much more of it penetrates shields (very good against shielded targets, mediocre against unshielded targets). Comes with standard Boff powers.
Chroniton: can slow down enemies. (nice for making enemies' weakened shields harder to protect, or as a rear launcher to use when running away). Comes with standard Boff powers.
Tricobalt: very high damage, and a short disable effect (stops target from using any powers for a moment). has a very long cooldown and doesn't get modified by Boff powers.
On Ground:
Phaser: Chance to stun
Disruptor: Chance to debuff damage resistances
Plasma: Chance to proc fire based DoT
Tetryon: Chance to proc Shield damage
Polaron: Chance to proc weapon disable
Anti-Proton: Bonus Crit damage
Hate the trash heap that is the Official Forum right now (hopefully they go to paying members only soon to get rid of most of the trolls), but there is an occasional nugget of gold in among all that dross.
This thread is one such nugget.
I personally roll with Dual Disruptor Beam Arrays, Photon Torpedoes, and Quantum Mines, but I've been thinking about Plasma Torpedoes (since they have been a subject of discussion in Fleet chat of late) and wondering if their ability would work with the BOff ability "Torpedo Spread". It could be very useful against groups of targets.