I forgot when's the last time I pirated in a fighter or a bomber.. That usually happens only when I'm on my way somewhere and trader just falls in my arms. Awesome, next nuclears are free! But even then I regret that Mentira isn't there.
As asno said, VIP, Gold, Niobium things like that. Engine components, diamonds sometimes (when they pass trough omegas). Usually I wait until my hold is full and sell away. I usually take the third of the hold, even though that sometimes might suck, for example if the entire run gives out 3mil, I ask for like 800k profit, and worst thing happens when there's no-one to peddle the goods so I sell them even cheaper. But it's a Pirate's life.
We tried to bring a special case when pirating the VIPs as we roleplay of taking the VIP person, not her escorts, or vice versa, depends on what the trader says VIPs are. (scientists, movie stars, important businessmen), and then we were looking at docking with a pirate ID on Kurile to ransom them back to their families/companies/wifes and things like that.
But eventually we decided to bring in our old friends OTC and give them cutt of the profit.