Better weapon combo?
 

Gloomwater Harpoon Primary w/

EBW or Sharkjaw Cutlass

for a rogue.

Are you not interested in the Burning Rapier quest or are we talking about a lowbie twink?

Regardless of what you choose to complement the Harpoon, I strongly suggest you check out this thread I spun off last week.

Long story short: there's a good chance the Harpoon is better suited for your offhand. The thread in that link has the long-winded details.