If you are looking for a free dating website, you could do worse than Flirtbox. Flirtbox is a site built with free dating and fun in mind. The site is bright and has a young-ish outlook, which is reflected in its audience. Late teens to late twenties is probably where its strength lies though it encourages all ages to join.
The dating truly is free and you can send and receive messages without making a payment or using a credit card or paypal. You can also browse as many members as you want as well. If you are looking for some flirty fun, then flirtbox is certianly the site for you.