Why do you need to promote your startup somewhere other than on the internet?
My (completely accidental) approach is:
1. Spend four years being heavily involved in open source development (FreeBSD in my case) and gain a reputation for producing really cool software (both FreeBSD Update and Portsnap have elicited reactions of "how did we manage to survive before this was available" from multiple sources).
2. Announce that I'm working on a new project.
3. Watch as emails flood in from users of my earlier works who are convinced that whatever I'm working on right now has got to be the best thing since sliced bread.
Of course, I haven't launched publicly yet, and I don't know how many these enthusiastic people will end up paying to use my current project -- but it certainly won't hurt to have an established reputation for doing cool stuff.