I would say writing articles and submitting them directories. This is free if you write the articles yourself. You will get some visitors and backlinks.
It varies product to product but normally as I had examine free e-book , newsletters and blogging give great traffic and conversions.
Have a list of opt-in prospects interested in the content related to the product and set it up in an email series using an auto-responder that targets that products niche. It's work that many won't want to do, but that's ok, more money for me and others like me who are willing to actually work to receive.
Agreed, if you use super targetted long tail keyword phrases rather than general catch-all keywords. The more targetted the keyword (e.g. 'buy blue honda iowa', as opposed to 'car'), the more likely your ad will convert into a click by the person most likely to be interested. It'll almost certainly be very cheap traffic too, since you will not have a lot of competition. In short, less traffic, but higher conversion. Make sure to split test your ads too, so you can make tweaks and improvements. Supplement this with articles, opt ins, heck make a video with your URL watermarked on it and stick in on YouTube, all these things will drive traffic and help build a brand.
You could also hire someone to post on related forums for you, with your signature pointing at your website
Post quality articles and blogs at free web services/blogging/groups/etc. If you can make/find some cool video related to your audience, that would make marvel for you as well.
The crappy 100,000 visitors for $5. However, if you are looking for quality traffic, I suggest word of mouth and google adwords.
Time is money - besides that these sites are free... Craigslist.org Digg.com Myspace.com Related Forums Blogs - post on Technorati.com StumbleUpon.com
Well, I would say Social Bookmarking sites & Forum signatures will bring you some targetted traffic for free or almost...
The cheapest ways I found: 1) Article submission 2) Blogging You will get tons of Google top 10 when you do this. It's working like gangbusters. You can find more in my free ebook here: http://forums.digitalpoint.com/showthread.php?t=329046&page=3
I use article marketing as my prime form of advertising for good reason. It builds backlinks for SEO, it helped me get on the front page of Google for many, many longtail keywords, and it drives targeted traffic through the resource box.
How about holding a drawing where someone gets the product for free? Make a press release and then make a special offer to all the other customers who submitted their information.