Combat Reflexes [General]
Benefit: You may make a number of additional attacks of opportunity equal to your Dexterity bonus.
With this feat, you may also make attacks of opportunity while flat-footed.
Normal: A character without this feat can make only one attack of opportunity per round and can't make attacks of opportunity while flat-footed.
Special: The Combat Reflexes feat does not allow a rogue to use her opportunist ability more than once per round.
A fighter may select Combat Reflexes as one of his fighter bonus feats.
A monk may select Combat Reflexes as a bonus feat at 2nd level.
Source: SRD 3.5 Feats