Reservation Manager Lite is a free to use and distribute rental system for Joomla. It allows you to easily publish your properties and take online reservations.

If you need more functionality such as PayPal integration, Front-end Availability Calendars, Multi-lingual capabilities then take a look at Reservation Manager PRO. For just 99 euros you get a full featured reservation system and as much support as you need to get your site up and running.