We've just started using a new system called Realbird, and although I was skeptical at first, it's a pretty useful system!
For no charge at all, you can load your listings into it and it will syndicate automatically to sites such as Zillow.com, Trulia.com, Hotpads.com, Local.com and a slew of others, including a few that are international!
In addition to the automatic syndication, it also lets you load your listings onto internet classifieds like craigslist.com, kijiji.com, backpage.com and oodle.com. It just takes the information that you gave it about the property and generates an HTML code for you to paste wherever you want, and it comes out to be a very attractive flyer with a lot more photos than craigslist.com will typically allow you to load. It even produces widgets, which are small ads for your listing that can be placed just about anywhere; blogs, facebook pages, myspace pages, etc...
It has a pretty user-friendly interface, you just fill out a form about your listing and upload your photos, then follow the on-screen instructions. As I said, I've just started using it, but I am impressed so far.
Just wanted to share this great tool!