Well, I'll admit to being a bit biased, but I would say search engine optimization (SEO) is one excellent form of marketing today. When people find you through search engines, they're already actively looking for something your business offers. You can't ask for a better lead than that! You can do a lot of the basics yourself, and it's well worth your time.
Getting involved in social media is another tool a business can use, but you have to be careful not to simply blast your products. To make social media really work, you have to give your customers reason to like you and stay with you. It's quite an investment of time and effort and only pays off in the long-term.
Finally, of course there's always Pay Per Click advertising like the kind you see at the top of Google and here on HubPages, but this can get expensive fast if it's successful as each click costs you money. It's important to make sure each click also leads to a sale to make up for that, so conversion optimization is needed alongside it.
Hope that helps!