gistfile1.php

<?php

add_filter( 'the_content', 'custom_before_content' );
function custom_before_content ( $content = '' ) {
	// Just drop in content in the your_text variable. It can be html or plain
	$category = get_the_category();
	switch( $category[0]->cat_name ) {
		case 'Category 1' :
			$your_text = 'Category 1';
		default :
			$your_text = 'Default';
	}
	return $your_text.$content;
}

add_filter( 'the_content', 'custom_after_content' );
function custom_after_content ( $content = '' ) {
	$category = get_the_category();
	switch( $category[0]->cat_name ) {
		case 'Category 1' :
			$your_text = 'Category 1';
		default :
			$your_text = 'Default';
	}
	return $content.$your_text;
}