this question always rares its little head in this forum

but here are the way which work best for me!

1 - Myspace - social networks (will be huge 2007)
2 - Search Engine Optimization
3 - articles
4 - Website Directories
5 - newsletters
6 - Free Viral Pdf - links embedded.
7 - affiliate program
8 - Blogs & or wordpress - daily posts
9 - PPC google adwords
10 - forums