EPA's Nonpoint Resources

Clean Water Act (CWA) § 319 Grant Program resources and guidance
Coastal NPS Program (CZARA)
Contact information for State NPS Management Programs
CWA § 319 Grants Reporting and Tracking (GRTS)
Healthy Watersheds Program (watershed protection)
Kids pages
Low Impact Development (LID)
News-Notes (NPS national newsletter)
Nonpoint Source homepage
NPS guidance for Federal Land Management in the Chesapeake Bay
NPS monitoring resources
NPS outreach and education
NPSINFO Resource Center
Outreach Toolbox
Success Stories 
Technical guidance for controlling NPS pollution 
Watershed planning handbook 
Category specific resources
Abandoned mine drainage, Agricultural, Hydro-modification, Forestry activities, Urban lands, and Wetlands and riparian areas
USEPA's watershed academy provides training and information on implementing watershed approaches.  It provides self-paced modules, webinars etc. from experts across a broad range of watershed topics.