Prueba agregando DISTINCT a la consulta:
Código:
<?php
$link = mysql_connect("localhost","root");
mysql_select_db("inmo",$link);
$consulta = mysql_query("SELECT DISTINCT edo2 FROM oper ORDER BY edo2 ASC",$link);
while($reg = mysql_fetch_array($consulta))
{
echo "<option value=\"$reg[edo2]\">$reg[edo2]</option>";
}
?>
</select>