Valueline is perhaps the best-known and most widely respected stock market advisory service in the U.S. The service tracks somewhere around 1700 stocks across 90 industries, and provides subscribers with a wealth of information about individual stocks as well as the overall economy.
A key component of Valueline is its rating system, which rates individual stocks on "Timeliness" and safety. The rating goes from 1 to 5, with 1 being highest. Since 1965, if you had done nothing but simply buy Valueline "Timeliness 1" stocks, you would have averaged 13.9% per annum, handily beating the S&P (which would have returned 6.8% per annum) and the DOW (which would have returned 6.4% per annum). There may be a few stock market advisory services that do better for 1 to 5 years, but Valueline is impressive because it has maintained this stellar performance for 40 years.
Through Dec. 2008. Chart taken from www.valueline.com
The service can be purchased in print format or as an online subscription. Subscribers also have access to 3 model portfolios they may follow if they do not wish to construct their own portfolios. Although Valueline offers many different products, the most famous one is the "Valueline Investment Survey" which gives you access to ratings and model portfolios, along with weekly market and economic commentaries.
Valueline is heavily used in classes taught at business schools and MBA programs. Ask any MBA (including me) what Valueline is, and they'll definitely know. That should give you a good idea of how highly regarded this service is, especially in the academic community. I rely on Valueline for a large portion of my stock market investments, and I recommend it highly.