Eagle's Eye

Prerequisites: Point Blank Shot*, Precise Shot, Rapid Shot, Dex 19

With a glance, you discern several telling weaknesses in your enemy's defenses.

Benefit: If an opponent within 30' is engaged in melee, make a Spot check as a Move Action* against a DC equal to the opponent's Armor Class. If successful, the opponent is flat-footed against your next attack*. This has no effect against creatures normally immune to Sneak Attacks.

Normal: Opponents engaged in melee are not treated as being flat-footed.

Credit: http://www.giantitp.com/forums/showthread.php?t=48255

_{* changes made by DM}