If you are a nature photographer, you might want to check out Great American Photography Workshops. GAPW has been in business for 15 years -- and they have a wide variety of classes from single day events to multi-day tours.

Here is the web-site:

http://www.gaphotoworks.com/

On the site you'll find information about upcoming events as well as articles written by GAPW instructors.

(BTW -- I really wish I could go to the Glacier National Park workshop in September -- Scott Kelby of the National Association of Photoshop Professionals will be there!)