Here are some free web marketing tips - http://www.small-business-software.net/free-web-marketing.htm
Be careful with PPC. You can easily lose more than you make when starting out. I recommend article submissions, directory submissions, pr submissions, good content on your site, backlinks, blogging, and Facebook.
Well if you are looking for the "best" way... The best way is to have a blog. It's evergreen and always there. It get's indexed, you own the content on it, you control the topic, etc. Then you can take a bunch of different methods (listed above by other posters) and advertise your blog. Another thing to consider is to add a link in your signature on forums such as this. Notice...I have a link to my website in my signature. This is not just free advertising...it's adding backlinks to my site which helps the search engine determine how to rank my site. Bottom line, the best way to promote a biz online is to establish a web presence. Doesn't matter if it's a static site or a blog. Just have something you can point people to. Update your site and add content. THEN worry about advertising. Your first step is in your web presence.
you should also consider using ucc sites..like youtube.com..Make your own video introducing your company or what you do and add it on the list. Make some interesting articles related to your business and submit to the article submission sites. and link it to bookmarking site..like digg.com and so on..worth to try!