Well, that can be difficult to say. If you are talking long-term as in 10 to 15 years from now, then its a matter of being able to see where technology and the world we live in is going in that time frame. The companies who are able to exploit what consumers will need/want 10-15 years from now will prove to be good long-term investments.
So think about what you were doing in the 1993-1998 timeframe. What was "in style", what were people doing for recreation? What were consumers buying for Christmas? Who were the companies selling those items? Now look at the financial performance of those companies since that time. Substantial investments in companies like Microsoft, RIMM, Google 10 years ago would make you very rich today.
Its a matter of principal (having some money to invest), patience (keeping that money invested), prophesy (seeing what will happen in the future based on what has happened in the past). Now i'm not talking "fortune-telling" when I talk of prophesy, I'm merely saying, as a consumer, you have most of the knowledge necessary to figure out what the world is coming to from a needs/wants perspective.
For example, I happen to think that in 10 years, because of rising fuel costs, traffic issues, and its effect on productivity, people won't be driving to work like they do today. Most people will be "home-based". So companies who can exploit that need early and make it easy for these individuals to work from home will do well 10-15 years from now. Well, what do you need when you work from home? High speed access at a low price, Video conferencing hardware/software, bio-security for document verification, etc. etc.
I also happen to believe that RFID implants will have become more acceptable to the public, especially in dealing with illegal immigration, terrorism and crime issues. If the U.S. made it manditory in order to become a "legal" citizen in the United States that those individuals most receive a "veri-chip", you better believe that they would. I want to be invested in the company that got the federal contract to provide those RFID chips. My bet is with a company called Digital Angel (DIGA). They are sitting at 61 cents a share right now. I'll have about 100,000 shares of that company within the next 4 years. When that stock hits $100 a share in about 10 years, that's $10 Million. Now that's what I call long-term!
Anyway, my point is, no one has a crystal ball. Long-term investments in solid companies with good business prospects now and in the future are always a good investment. I still kick myself about RIMM because I SAW how cool those "2way" devices were when the stock was $2 a share back in 1999 and never budged. Not letting that happen again.
Let's get it.