To expand on Nail's suggestions...
Because you're going with a Brawny Rogue, you want an at-will that will take advantage of your Strength score. Looking at the at-wills in the PHB, Riposte Strike uses Strength for a secondary effect.
Sly Flourish probably won't be as useful since it relies on Charisma. That narrows down your options to Deft Strike for mobility, or Piercing Strike so that you can attack Reflex. Of the two, Deft Strike is generally regarded as the better option, since Rogues in 4E really need to be moving around.
One thing to note about Deft Strike is that the bonus movement counts as a "move," and not a "shift." If you "move" next to an enemy, you'll take attacks of opportunity; "shifting" negates that. Because of this, the best use for it is, IMO, to get a little extra range to make it to an enemy.
If you have Martial Power, Disheartening Strike is worth a look. However, personally I favor Deft Strike because of the movement.