There are several ways available online that you could use to promote your blog without spending a single penny. But you need to put in a bit of hard work so that you get a good response. The ways are
1. Participate in community forums like blogger forum.
2. Participate in groups like google groups and yahoo groups
3. Participate in social networks like digg, reditt, orkut,facebook etc.
4. Participate in entrecard
5. Write as a guest writer in other blogs
6. Comment on follow on blogs
7. Submit a press release in PRBUZZ, PR.COM,PR FREE etc.
8. Use free advertising in Sales Spider, Kijiji, ABC Sreach etc.
9. Participate in contests and giveways
10. Start a free giveway for blog
11. Apply for website awards and blogger choice awards.
12. Start a podcast
13. Give free ad spaces to other bloggers
14. Start a contest in blog