Denied actions or denied combat options are pretty much the bread and butter of control.

Bestow Curse. People tend to discount it quickly. Fail the save though, and you get a choice of options. Neg on attacks, impact to abilities, or 50% to even get an action that round, and even if they do get an action, it is a move OR standard action, not both.
If I recall correctly there is another debuff that gets the same result. Exausted I think? If you can pull off such a debuff in an AoE, you're laughing.