It's not that easy to find sites that let you advertise your holiday home for free, but I have found a few and I have listed them here. By far the most practical is gumtree as you can actually put photos and links to your website.
Craigslist is almost as good as gumtree. I think it is still very much biased towards the US market.
Google base is quite handy but in most item listings there is an expiry date. I did find one category that did not expire.
Gite-directory is quite good too and the webmaster is very friendly. The submission and modification of info is not that straight forward unfortunately. The site does say it protects your email from spam and sends you any enquiry emails without problem.
I was very impressed with the self-catering-breaks site that makes it very flexible and easy for changing photos and general information. The enquiry email works brilliantly.
I would rate holidaylease second as it puts paid advertisers on the same page as your add, but it does provide a calendar for your bookings which can be quite handy.
Then, there is the whole range of local classified adds like loot.com and exchange.co.uk that let you put a few words on their site. They don't usually let you put a link to your website but they usually let you provide an email address. Unfortunately, I found that the add and email were hijacked on glasgow-times.com and diverted to another ad.
Freewebsitedirectory allows you to put a link to your website with a description line or two.
http://www.frenchentree.com/ is a new one that says you can advertise for free but it is very difficult for users to browser as it is overloaded with info and advertising.
The HomeIsAway website lets you advertise for free for one year. Either you pay for the link to your site or you provide a link from your site to theirs and you get the link for free. That defeats the point though.
rent-holiday-home does not let you put a link to your site but you can upload images and text and locate your property on a map.