This code will give the users a capablity to choose, how many elements(items) they can display on the views page. Just create a module and configure array values and its done. The code uses the views header section to display the number selection menu.
View name is the name of the currently opened view.
You will find your page id at the end of your view url, right next to views-tab-, after you have opened your current tab in the new window. This will look something like that: admin/build/views/edit/youre_view_name#views-tab-page_id .

function modulename_views_pre_execute( &$view ) {

	#Configuration start

	# set array values view_name => page_id
	$views_data = array(
		'newest_books'	=> 'page_1',
		'bestprice'		=> 'page_1',
		'taxonomy_term'	=> 'page',
	);

	#Set number of items to show
	$numbers_to_show = array(5 ,25 ,100);
	
	#Configuration end

	$page_id = $views_data[ $view->name ];
	if( ! $page_id ) { return; }

	$view_url_path = $view->display[$page_id]->display_options['path'];
	$vupc = strlen($view_url_path);
	$page_path = substr($_GET['q'] , 0, $vupc);
	if( $page_path != $view_url_path ) { return; }
	
	# Create links
	$items_per_page = array();
	foreach( $numbers_to_show as $nr ) {
		$items_per_page[] = l( $nr, $_GET['q'], array( 'query' => "items=$nr" ) );
	}
	$header = t('Items per page') . ': ' . implode( ' | ', $items_per_page );

	# hack the view
	$default_count = $view->display[$page_id]->handler->default_display->options['items_per_page'];
	$selected_count = $_GET['items'];
	$handler = &$view->display[$page_id]->handler;
	$handler->set_option('header', $header);
	$handler->set_option('header_format', 2);	

	# set items per page
	$view->set_items_per_page( $_GET['items'] > 0 ? $selected_count : $default_count );

}