There are a number of newer methods of marketing which really should be classed as PR (Public Relations). As with most such ideas they are 98% hype. Here's a quick rundown of what they are and what is or isn't valid about them.
"Cause marketing" refers to getting the word out about your company or products and hopefully creating a positive attitude by promoting some cause - environmentalism is huge currently. Any product or service which can call itself "green" has a leg up these days as a large percentage of people actively support such efforts. But by itself this kind of thing will neither make you well known nor popular.
"Buzz", "Stealth" or "Underground" marketing are all terms used to refer to efforts to get word-of-mouth going by paying people to do things like go into bars and talk up or use the product. These are rarely successful. If a product isn't going to go viral, it isn't going to go viral.
Underground marketing can also refer to the likes of product placement in movies and TV shows, and sponsoring of events (think "Flugtag") of the right sort. Inherent in the concept is there is no real advertising type push or sales pitch. Instead, they depend on placing the product in the right light amongst opinion leaders in the target market - the small percentage of people who will spread not just the word but create the right attitude towards the product.
These can in fact work well with good research, planning and execution. Without any big advertising spend, purchasing your product becomes the thing to do. Toyota's Scion has been notably successful with this.