Two of the more hellish creations I've come up with are the Mega Particle Cannon and the Quad Plasma Streamer. Here's the numbers on both of them.
Mega Particle Cannon
Class: Particle
Mode: Raking (20)
Damage, 3 turns: 3D10+30
Damage, 5 turns: 6D10+60
Damage, 7 turns: 9d10+90
Range Penalty: -1 per 4 hexes
Fire Control: +7/+5/+3
Intercept Rating: N/A
Rate of Fire: Variable, See Above
Power to Arm: 12
Quad Plasma Stream
Class: Plasma
Mode: Raking (5)
Damage: 12D10+16 (-4 per hex)
Range Penalty: -1 per hex
Fire Control: +2/+2/-4
Intercept Rating: N/A
Rate of Fire: 1 per 2 turns
Special: Each sub-volley is mitigated by armor, and each full sub-volley which strikes a system degrades armor there by 1 point permanently
Power to Arm: 16