Check out some of these sites, they are pretty informative and very pertinent to what we do at GDL.

Drumline.com

Marching.com An extensive source of information for all things Marching-- band,corps, etc.
Pretty self-explanatory, eh?

Drum Corps International The source for information about the latest in drum corps happenings.
Bands of America BOA is to high school marching bands what DCI is to the world!
A great source for marching band related events across the country.
Percussive Arts Society The definitave source for all things percussion.