Free trafic - Blog commenting

Find blogs in your niche and leave real comments on them (don't spam, leave real USEFUL comments) along with a link to your website. This will bring free trafic to your website. It will also give you backlinks (good for search engines)

Free trafic - Social bookmarking

Bookmark your website at all the social bookmarking sites.
Use: http://www.onlywire.com/ to save time and bookmark at several sites at once.

Free trafic - Video

Video is a great way to attract a flood of free trafic to your website. Upload an interesting video you created yourself to: http://www.youtube.com/
Don't forget to have a link to your website in both the video itself and in Youtube's description field (including http://)

Free trafic - Articles

Articles is a great way to get lots of free trafic without spending a cent. Write an article about your niche, hobby or interest. Add a resource box at the end (this is where you link to your website)
Submit the article to:
http://www.ezinearticles.com/
(note: they're quite picky, so if you're submitting for the first time be prepared to change the article according to their recommendations)