It depends on your product... who are you marketing to? If your product is targeted at the masses, certain things will work (such as social media), but if you're targeting a market such as military or government agencies, that wouldn't work at all. You'd have to advertise in ways that would appeal to them directly (military trade shows, ads in military related magazines/websites, etc.). So it really has to depend on your audience.
After you finish your project, what type of marketing do you use to make it popular?
...and by the way, if you're waiting until you're finished with a project to market it, you're already too late. Smart marketing starts while you're still working on the project, usually somewhat in the mid to early stages (some wait until the late stages but then you'll be limited in changes at that point). Why? You need to build hype AND get some immediate feedback from users as to what they would like to see your product do. How? They'll say "Cool! ...but does it also do this..." and you'll learn what it is they expect.
It depends on the type of the product you're about to release but I think it would be best if you can combine several marketing tools rather than using just one. In nowadays situation, social media would be the most efficient tool to spread the reputation of your product.
When trying to make your product or project popular, you have to ask yourself, to whom are you trying to cater your product to? Is it the masses in general? Or is it a more specific group of people? Usually a social networking and social media is a notably very helpful aid in creating traffic for your product. But different advertisements work for different different groups of people.
Yes its SEO...and social media now a days if you have time and patience for your results to come up. Otherwise we go with SEM i.e. search engine marketing which includes all the paid techniques to bring business. It includes PPC, CPC and more.