Simply a pop-up form element of all 50 US States. Save you creating your own.

            <select name="state">
              <option value="" selected="selected">Select a state...</option>
              <option value="AL">Alabama</option>
              <option value="AK">Alaska</option>
              <option value="AZ">Arizona</option>
              <option value="AR">Arkansas</option>
              <option value="CA">California</option>
              <option value="CO">Colorado</option>
              <option value="CT">Connecticut</option>
              <option value="DC">District of Columbia</option>
              <option value="DE">Delaware</option>
              <option value="FL">Florida</option>
              <option value="GA">Georgia</option>
              <option value="HI">Hawaii</option>
              <option value="ID">Idaho</option>
              <option value="IL">Illinois</option>
              <option value="IN">Indiana</option>
              <option value="IA">Iowa</option>
              <option value="KS">Kansas</option>
              <option value="KY">Kentucky</option>
              <option value="LA">Louisiana</option>
              <option value="ME">Maine</option>
              <option value="MD">Maryland</option>
              <option value="MA">Massachusetts</option>
              <option value="MI">Michigan</option>
              <option value="MN">Minnesota</option>
              <option value="MS">Mississippi</option>
              <option value="MO">Missouri</option>
              <option value="MT">Montana</option>
              <option value="NE">Nebraska</option>
              <option value="NV">Nevada</option>
              <option value="NH">New Hampshire</option>
              <option value="NJ">New Jersey</option>
              <option value="NM">New Mexico</option>
              <option value="NY">New York</option>
              <option value="NC">North Carolina</option>
              <option value="ND">North Dakota</option>
              <option value="OH">Ohio</option>
              <option value="OK">Oklahoma</option>
              <option value="OR">Oregon</option>
              <option value="PA">Pennsylvania</option>
              <option value="RI">Rhode Island</option>
              <option value="SC">South Carolina</option>
              <option value="SD">South Dakota</option>
              <option value="TN">Tennessee</option>
              <option value="TX">Texas</option>
              <option value="UT">Utah</option>
              <option value="VT">Vermont</option>
              <option value="VA">Virginia</option>
              <option value="WA">Washington</option>
              <option value="WV">West Virginia</option>
              <option value="WI">Wisconsin</option>
              <option value="WY">Wyoming</option>
            </select>

Simple one-trick-pony PHP function to take a state name (case insensitive) and return the 2 letter abbreviation.

	function state_to_twoletter( $state_name ) {
		
		$state = array();
		$state['ALABAMA']='AL';
		$state['ALASKA']='AK';
		$state['AMERICAN SAMOA']='AS';
		$state['ARIZONA']='AZ';
		$state['ARKANSAS']='AR';
		$state['CALIFORNIA']='CA';
		$state['COLORADO']='CO';
		$state['CONNECTICUT']='CT';
		$state['DELAWARE']='DE';
		$state['DISTRICT OF COLUMBIA']='DC';
		$state['FEDERATED STATES OF MICRONESIA']='FM';
		$state['FLORIDA']='FL';
		$state['GEORGIA']='GA';
		$state['GUAM']='GU';
		$state['HAWAII']='HI';
		$state['IDAHO']='ID';
		$state['ILLINOIS']='IL';
		$state['INDIANA']='IN';
		$state['IOWA']='IA';
		$state['KANSAS']='KS';
		$state['KENTUCKY']='KY';
		$state['LOUISIANA']='LA';
		$state['MAINE']='ME';
		$state['MARSHALL ISLANDS']='MH';
		$state['MARYLAND']='MD';
		$state['MASSACHUSETTS']='MA';
		$state['MICHIGAN']='MI';
		$state['MINNESOTA']='MN';
		$state['MISSISSIPPI']='MS';
		$state['MISSOURI']='MO';
		$state['MONTANA']='MT';
		$state['NEBRASKA']='NE';
		$state['NEVADA']='NV';
		$state['NEW HAMPSHIRE']='NH';
		$state['NEW JERSEY']='NJ';
		$state['NEW MEXICO']='NM';
		$state['NEW YORK']='NY';
		$state['NORTH CAROLINA']='NC';
		$state['NORTH DAKOTA']='ND';
		$state['NORTHERN MARIANA ISLANDS']='MP';
		$state['OHIO']='OH';
		$state['OKLAHOMA']='OK';
		$state['OREGON']='OR';
		$state['PALAU']='PW';
		$state['PENNSYLVANIA']='PA';
		$state['PUERTO RICO']='PR';
		$state['RHODE ISLAND']='RI';
		$state['SOUTH CAROLINA']='SC';
		$state['SOUTH DAKOTA']='SD';
		$state['TENNESSEE']='TN';
		$state['TEXAS']='TX';
		$state['UTAH']='UT';
		$state['VERMONT']='VT';
		$state['VIRGIN ISLANDS']='VI';
		$state['VIRGINIA']='VA';
		$state['WASHINGTON']='WA';
		$state['WEST VIRGINIA']='WV';
		$state['WISCONSIN']='WI';
		$state['WYOMING']='WY';

		// Canadian Provinces
		// edited 12-5-07
		$state['ALBERTA']='AB';
		$state['BRITISH COLUMBIA']='BC';
		$state['MANITOBA']='MB';
		$state['NEW BRUNSWICK']='NB';
		$state['LABRADOR']='NL';
		$state['NEWFOUNDLAND]='NL';
		$state['NORTHWEST TERRITORIES']='NT';
		$state['NOVA SCOTIA']='NS';
		$state['NUNAVUT']='NU';
		$state['ONTARIO']='ON';
		$state['PRINCE EDWARD ISLAND']='PE';
		$state['QUEBEC']='QC';
		$state['SASKATCHEWAN']='SK';
		$state['YUKON']='YT';

		return $state[strtoupper( $state_name )]; 
		
	}