SCOUNDREL CLASSES -
Bard
Scout
Spellthief
Ninja
Rogue
Swashbuckler
Beguiler
Lurk
Monk
Ranger (maybe)
So, you got a pretty broad range of classes to choose from, there. Add a few healing things to the bard, to make them the cleric class, and you actually have all four major food groups represented - combat types, skill monkeys, buffers, and arcanist.
as for what the group actually *does*, why not use all that wonderful advice in the back of Scoundrel? Or, better yet, watch those spy movies, like Ronin, Spy Game, the Bourne Identity, or pretty much any Tom Clancy novel.
Hell, imagine an Eberron game where the group learns that one of the big bad sects has uncovered an unused House Cannith weapon from the Last War - something that will make another Mournland. It pretty much becomes "The Sum of All Fears" - trace where the "nuke" came from, and then try to stop the baddies before they can get it off.
That's a pretty good campaign right there, and it plays perfectly for scoundrel characters.