What is the most cost effective method of getting your message across to potential customers?
That really depends on your target market, as, for example, you may not find a large number of engineers using Twitter, but if you are aiming for college students then that could be useful.
If you are aiming for a group that is local, perhaps in Wichita, KS, then newspaper and radio may still be useful.
But, regardless of the medium, being creative is best.
For a good example, look at the Budweiser commercials and the stock company with the baby, in the Superbowl. These are incredible commercials.
You can also look at many of the viral videos, and see what is helping to draw people to these. If you come across as just another company, then you will be easily ignored, and in some mediums you will be seen as just annoying spam.
Youtube could be an amazing way to get your brand out, but, again, you have to be able to stand out from the crowd.
So, work on your concept, after you narrow down to whom you want to reach out to, and then your medium will become more obvious.