If the new economy, the last Big Thing, failed to separate your from your last penny, then Mark Howdle, a European equity strategist at Schroder Saloman Smith Barney Inc., would like to propose for consideration the Next Big Thing : Eco-tech. "The concept is quite simple," Mr. Howdle wrote in a report on the subject. "It encompasses the production of energy from clean or renewable sources; or a cleaner or more efficient use of energy, however created."