You gain a +4 haste bonus to your AC. Thus, if your AC is 15 (+4 chain shirt, +1 dex), it is now 19 (+4 chain shirt, +1 dex, +4 haste). You lose this bonus to your AC whenever you would lose a dodge bonus.
Your jump distances are multiplied by 1.5.
You get an additional partial action each round, either before your normal action or after it. What you can do in a partial action is listed in the PH on page 127. For instance, you may make a single melee or ranged attack or cast a 1-action spell. Remember, this is in addition to your normal action in a round. Thus, a hasted wizard can move his speed and cast a 1-action spell, then cast another 1-action spell for his partial action.