Support forums and FAQ. You can even combine the two by stickying your FAQ in the forum.

Ticketing systems just plain suck. If no one else can see the questions/answers then I see no point. Perhaps for paid support they're okay, but certainly not for free support. For free support you need to make sure you can keep your support load as tiny as possible and so having a massive stock pile of previously answered questions can make a huge difference to reducing the support you need to offer.

Blog posts are stupid place to provide support unless you only have a tiny number of support questions being asked. I refuse to answer any questions in my blog posts and having to rifle through hundreds of support questions in blog posts is a nightmare.

I ended up with over 1000 support questions on the blog post for my first ever WordPress plugin. It only took a month or two before I purchased another domain and plonked a forum on it to rid my blog of the annoying number of comments.

I'm also thinking of branching out into video-tutorials as some people don't seem to be able to understand simple instructions in textual form.