Although it's not free as the original post requested, I can also recommend Rapidweaver, it's the best compromise between ease of use, standard of finished site and flexibility that I've found in a WYSIWYG site builder.
I've tried iweb, sandvox and freeway but I like RW the best.
If you visit screencasts online they have 3 very good tutorials on how to use the software and even had a discount code to save money on the software!
You can get a very nice basic site up and running within half an hour, if you spend a little more time and use some of the plugins available you can get very professional looking results, I only recently started using it as I read a review in 'mac format' magazine which only gave it 3 out of 5, but they failed to mention the great plugins available from
http://www.yourhead.com/ , they only cost a few quid each and add alot of extra functions and ease of use to RW.
The only downside is the pages aren't totally customisable, at least not unless your create your own html which defeats the point of a wysiwyg builder, but I've seen guides on how to customise RW themes and there are plenty available to download and buy.
To be honest I think if you don't know anything about html (like me) and if you've not got the time or the interest to learn it but want to create a stylish site without the hassle then you would be better spending a few quid on software like this.
(it's also much more advanced than iweb !)