Reactive Counterspell( Magic of Faerûn, p. 22)
You can react quickly to counterspells cast by opponents.
Improved Initiative (PH) , Improved Counterspell,
Once per round, you can counterspell an opponent's spell even if you have not readied an action to do so. This counterspell action takes the place of your regular action for the round. You can't use this feat when flatfooted.
Without this feat, you must ready an action each round you wish to use a counterspell (see the Player's Handbook, page 152).