Almanacs
Still one of the best tools for long-range weather forecasting; here's links from About.com's Weather website.

How to Make a Long-Range Weather Forecast
Excellent resource article at About.com's Weather website, with links to sites that make forecasts.

Weather Planner
Promises "a proven, reliable view of the weather up to a year in advance, so you can choose the best weather for your wedding, vacation, or special event." Try a free 30-day forecast; then for $9.95 register for a two-week forecast for anytime in the coming year.

More Weather Links
Short-term forecasts, current conditions, ski weather, weather risks such as hurricanes.