The promotional mix, which is the overall range of techniques available to the marketer, comprises many elements but I am going to focus here on Internet marketing: products distribution, information and promotional benefits to consumers and businesses through internet technologies. Internet promotion is very convenient for a developer on a low budget (global reach at relatively low cost, metrics, dialogue with users, avoiding the necessity for intermediary salespeople...). The main ways to go about it include:

Online advertising: advertising your products by posting links and banners across the web, on your partners websites or through ad networks like Google Adwords.
Search engine optimization: maximizing your chances of being found by search engines (most importantly Google) and be showed among the very first results. There are many methods that helps, like mentioning relevant keywords in your page text and meta data. Also, getting popular by getting people to mention your product online and link to it.
Social media: the use of social network sites and blogs to get in direct contact and interact with your customers and potential customers
This ends our series of articles on "marketing for programmers". There is a lot to say on this topic, but I wanted to stick to some key points related to the software industry. If you are already a black belt ninja marketer type, you would probably find most of those notes boring, sorry about that, but please let me know the important things that I missed here. Anyway, those notes were mostly a summary of things I wish I would know earlier. If you are a white belt, new to marketing and want to know more, you should check out "Foundations of Marketing" by David Jobber and John Fahy.
Thanks for reading.