Trend forecasting companies employ more designers then fashion houses. Fashion houses and independent designers do not publicly admit using trends forecasters...
They summarise top designer fashion shows and street wear. This specific website lives on the subscription basis (prices start at over £500 per 3 months of full access to the website).
They give a broad overview of trend coverage on colors, materials, clothing, graphics and accessories. They provide inspirational visuals, material for the mood, color boards and images from the catwalk shows and streets.
The TRENDSTOP (click the title to visit their website) is just one example which caught my eye whilst I was browsing the web and there are a lot of them (share the information on this if you found something amazing!).
Many forecasting companies put together style books and specification of prevailing and emerging styles, with predictions, suggestions for the next season.
New trends, according to Sue Jenkyn Jones (the author of "Fashion Design"), are supposed to arise from three main sources: high culture (fine art, classical music, theatre and so on), pop culture (TV, celebrities, music, movies) and low culture (activities pursued locally by special-interest groups, for example skateboarding).
The online Vogue home