[Catalog/Product] - Create product attribute - multiselect

CreateProductAttribute.php

<?php 

// Used for multi select
$installer->addAttribute('catalog_product', "hair_style", array(
	'group'                      => 'Your Group',
	'type'                       => 'varchar',
	'input'                      => 'multiselect',
	'label'                      => 'Hair Style',
	'visible'                    => 1,
	'sort_order'                 => 20,
	'required'                   => 0,
	'user_defined'               => 0,
	'searchable'                 => 0,
	'filterable'                 => 0,
	'comparable'                 => 0,
	'used_in_product_listing'    => 1,
	'visible_in_advanced_search' => 1,
	'is_configurable'            => 0,
	'global'                     => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
	'backend'                    => 'eav/entity_attribute_backend_array',
	'option'                     => array(
		"values" => array(
			0 => "Straight",
			1 => "Wavy",
			2 => "Curly",
		)
	)
));

//For single select attribute
$installer->addAttribute('catalog_product', "hair_special_needs", array(
	'group'                      => 'Your Group',
	'type'                       => 'int',
	'input'                      => 'select',
	'label'                      => 'Hair Special Needs',
	'visible'                    => 1,
	'sort_order'                 => 50,
	'required'                   => 0,
	'user_defined'               => 0,
	'searchable'                 => 0,
	'filterable'                 => 0,
	'comparable'                 => 0,
	'used_in_product_listing'    => 1,
	'visible_in_advanced_search' => 1,
	'is_configurable'            => 0,
	'global'                     => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
	'backend'                    => 'eav/entity_attribute_backend_array',
	'option'                     => array(
		"values" => array(
			0 => "Sulfate Free",
			1 => "Paraben Free",
			2 => "Anit-Humidity",
			3 => "Gluten Free",
			4 => "UV Protectant",
			5 => "None"
		)
	)
));

//Used for boolean attribute
$installer->addAttribute('catalog_product', "hair_sale_bag", array(
	'group'                      => 'Your Group',
	'type'                       => 'int',
	'input'                      => 'boolean',
	'label'                      => 'Sale Bag',
	'visible'                    => 1,
	'sort_order'                 => 1000,
	'required'                   => 0,
	'user_defined'               => 0,
	'searchable'                 => 0,
	'filterable'                 => 0,
	'comparable'                 => 0,
	'used_in_product_listing'    => 1,
	'visible_in_advanced_search' => 0,
	'global'                     => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
	'source'                     => 'eav/entity_attribute_source_boolean'
));

// Used for images attribute
$installer->addAttribute('catalog_product', "image_attribute", array(
	'group'                      => 'Your Group',
	'type'                       => 'varchar',
	'input'                      => 'media_image',
	'label'                      => 'Awards Icon',
	'visible'                    => 1,
	'sort_order'                 => 801,
	'required'                   => 0,
	'user_defined'               => 0,
	'searchable'                 => 0,
	'filterable'                 => 0,
	'comparable'                 => 0,
	'used_in_product_listing'    => 0,
	'visible_in_advanced_search' => 0,
	'global'                     => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
));

//Text Area type
$installer->addAttribute('catalog_product', "hair_questions", array(
	'group'                      => 'Sexy Hair',
	'type'                       => 'text',
	'input'                      => 'textarea',
	'label'                      => 'Hair Questions',
	'visible'                    => 1,
	'sort_order'                 => 999,
	'required'                   => 0,
	'user_defined'               => 0,
	'searchable'                 => 0,
	'filterable'                 => 0,
	'comparable'                 => 0,
	'used_in_product_listing'    => 0,
	'visible_in_advanced_search' => 0,
	'wysiwyg_enabled'            => 1, // IF used wygwys
	'global'                     => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_STORE,
));

Remember setup module class is Mage_Catalog_Model_Resource_Setup

<resources>
      <custom_setup>
           <setup>
                <module>Forix_Custom</module>
                    <class>Mage_Catalog_Model_Resource_Setup</class>
                </setup>
                <connection>
                    <use>core_setup</use>
                </connection>
       </custom_setup> 
</resources>