Category Ajax Chain Selects Shortcode: http://www.doitwithwp.com/a-shortcode-for-using-category-ajax-chain-selects/

gistfile1.php

<?php

function chain_select_shortcode( $atts ) {
	extract( shortcode_atts( array( 'tax' => 'category', 'level' => 1, 'titles' => array( 'Please select…' ), 'labels' => '', 'btn_text' => 'Submit', 'exclude' => '', 'count' => 1 ), $atts ) );

	return chainselect_getcategories( $tax, $level, explode( ', ', $titles ), explode( ', ', $labels ), $btn_text, $exclude, $count );
}

add_shortcode( 'ajax_chain_select', 'chain_select_shortcode' );