Have you considered going to software portals that provide software downloads / listings and getting your product listed? Places like CNET, Tucows and Softpedia. 
SEO isn’t really promotion as much as it is making your website friendly to the search engines. That being said, if you’re looking for promotion ideas you may want to look into Google AdWords. A fairly small budget could take you a long way if it’s properly setup.
If you could get bloggers to review your software and review your product it could go a long way for you in terms of links and boosting your ranking.
There are lots of way for promotion in SEO. You can start promoting your site in some new channels like facebook, twiiter, web 2.0 sites like hub pages, squidoo lenses and other good stuffs.
Using social networking sites is a big help in marketing your business such as facebook, twitter, etc. Visiting this sites regularly and posting interesting offers of your site can also help to drive traffic to your site.
There are several ways you can market your site.
Set up a Facebook Fan Page.
Write articles and submit them to article sites like Ezines.com.
Guest post on business blogs.
Post to sites like slideshare.com or docstoc.com.
Be a regular on Yahoo Answers…answer questions in your niche.
Comment on blogs in your niche.
Your all points are very important and useful. Thanks for nice information. i am working on Ezine but i am also working in Squidoo and Hubpages. I am getting good traffic from these sites.
Use social networking sites for website promotion. this is the one of the good way to promote websites.