Alistair is easy to set up as a good tank, I guess. Then Leliana and Zevran as rogues could do a lot of damage - or you could switch one of them for another warrior - probably Oghren - if you think you need a backup tank. Wynne for healing/offensive spells.
I'd do something like that and just make a char to replace one of them. I'd probably like to replace Wynne with my own mage, but rogue seems fun too. With paralyze runes on and a double weapon spec setup, they must be deadly
(there's that talent that let's them backstab stunned/paralyzed/prone enemies)