You need to put this script under shell/ directory in you Magento folder and adjust the constants to sweet your needs.

magento_dummy_simple_products_generation.php

<?php

// env config
ini_set('display_errors', 1);
umask(0);

// mage setup
require_once dirname(__FILE__).'/../app/Mage.php';
Mage::app()->setCurrentStore(Mage_Core_Model_App::ADMIN_STORE_ID);


// input values
define('CATEGORY_ID', 4);
define('PRODUCT_QTY', 15);
define('IMAGES_PER_PRODUCT', 1);
define('IMAGE_API', 'http://lorempixel.com/700/700/technics/');

// make an array with all websites
$website_ids = array();
foreach (Mage::app()->getWebsites() as $website)
	$website_ids[] = $website->getId();


for ($i = 0; $i < PRODUCT_QTY; $i++)
{
	srand(500+$i);
	$lorem_text		= 'Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Aenean commodo ligula eget dolor. Aenean massa. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Donec quam felis, ultricies nec, pellentesque eu, pretium.';
	$dummy_text['lipsum']	= str_shuffle($lorem_text);

	$dummy_title 		= substr($dummy_text['lipsum'], 0, 30); 
	$dummy_shortdescr 	= substr($dummy_text['lipsum'], 31, 220); 
	$dummy_descr 		= substr($dummy_text['lipsum'], 221); 
	$dummy_sku 		= substr(str_shuffle('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'), 0, 10); 
	
	$rand_price 		= rand(10, 999);
	$cost_price 		= rand(10, ($rand_price/2));
	$special_price 		= rand($cost_price, ($rand_price/2));
	
	
	$product = Mage::getModel('catalog/product');
	$product->setData(array(
		'name'				=> $dummy_title,
		'sku'				=> $dummy_sku,
		'short_description'	=> $dummy_shortdescr,
		'description'		=> $dummy_descr,
		'price'				=> number_format($rand_price / 10, 2, '.', ''),
		'cost'				=> number_format($cost_price / 10, 2, '.', ''),
		'weight'			=> number_format(rand(1,10), 2, '.',''),
		'status'			=> Mage_Catalog_Model_Product_Status::STATUS_ENABLED,
		'visibility'		=> Mage_Catalog_Model_Product_Visibility::VISIBILITY_BOTH,
		'type_id'			=> Mage_Catalog_Model_Product_Type::TYPE_SIMPLE,
		'tax_class_id'		=> 2,
		'attribute_set_id'	=> 4,
		'category_ids'		=> array(CATEGORY_ID),
		'website_ids'		=> $website_ids,
	));
	
	
	if ($i%4 == 0) // give some products a special price
	{
		$product->setSpecialPrice(number_format($special_price / 10, 2, '.', ''));
	}
	
	$product->setStockData(array( 
		'is_in_stock' => 1, 
		'qty' => 99,
		'manage_stock' => 1,
	)); 
	
	try {
		$product->save();
	} catch (Exception $e) {
		echo "ERROR: {$e}\n";
		die();
	}
	
	$product_id = $product->getIdBySku($dummy_sku);
	$product = Mage::getModel('catalog/product')->load($product_id);
	
	mkdir('tmpimage', 0777);
	for ($j = 0; $j < IMAGES_PER_PRODUCT; $j++)
	{
		// download and save file
		$image_source 	= file_get_contents(IMAGE_API);
		$image_name 	= dirname(__FILE__)."/tmpimage/{$dummy_sku}}_{$j}.jpg";
		file_put_contents($image_name , $image_source);
		chmod($image_source, 0777);
		
		try {
			$product->addImageToMediaGallery($image_name , ($j==0) ? array( 'thumbnail', 'small_image', 'image' ) : null, true, false );
		} catch (Exception $e){
			echo "ERROR: {$e}\n";
		}
		
		unlink($image_name);
		unset($download);
	}
	
	try {
		$product->save();
	} catch (Exception $e) {
		echo "ERROR: {$e}\n";
	}
}