Idealist - Volunteer, work, and intern job search
Huntathon - Browse and submit Product Hunt Global Hackathon projects
Idea Hunt - Solve specific challenges for your favorite products
CoFoundersLab - Meet 250,000+ entrepreneurs online
OpenVC - 2200+ VC firms by thesis to find 'best fit' for your startup
Foundler - Online hackathon weekends. Attend every other week.