depend on the level.
lower levels a summon is always good as it attacks your enemies even if you do not tell it to.
in higher levels the shadow gambit feat can make a real nasty surprise when combined with the 6th level permanent illusions (programed and permanent), and i't versatile too so it can deal p\b\s damage and focus on to hit or save to avoid to tailor it to the target. best part? it's already casted before hand so it doesn't betray the user when activated (my favorite were flocks of big nasty birds, hanging about until they attack)
it can be used with lower level illusions as well, but then you might have to keep concentrating on them to keep their duration. and you can't really have more then one ready.
beside that since were talking rogues and such. you might want to look into traps and the cunning trigger rogue talent.
a funny way to deal untraced attacks is a calamity caller warpriest class ability. bonus points if he look crazy and mumbles 'the end is near!' (although then it's kinda obvious who the one doing the calling might be)