Hacker News has a recent question about what it takes to market a startup to non-techies… I was at the NWEN Think Tank event last night and Nick Hanauer (early investor in Amazon, InSitu, Aquantive, among others) had a simple rule. Don’t spend money on Marketing. Simply put, great products and services usually speak for themselves.
I am not convinced that this is entirely true, but I completely agree with the fact that the best marketing in the world won’t sell a pile of crap. However, the best products sell themselves, even with horrible marketing…

It might be *sales* that’s unnecessary, not *marketing*. Great products sell themselves (i.e. don’t need goons to push customers) but it won’t make people know about you.
Yes, there’s word-of-mouth. But: (1) That spreads slowly until critical mass is achieved, and (2) some products are built to be easily spread, but I think it’s fair to say that means marketing has been built into the product (i.e. on top of the core functionality).
I also agree that marketing doesn’t necessarily mean spending money, especially nowadays. We spend money, but we also measure it carefully. Some info about how we do that in written form:
http://blog.asmartbear.com/blog/2008/4/14/agile-marketing-interview-at-geekaustinorg.html
And in a 6-minute-40-second video presented at Joel Spolsky’s Business of Software 2008:
http://blog.asmartbear.com/blog/agile-marketing-the-movie.html