Network For Good
Is a great site for giving and volunteering. The founding organizations are a who's who of big tech business. A good place to start your search for giving.

TeamKids
This organization is local to Southern CA, however, they do amazing work with Elementary age children. They get children involved in creating , managing and executing service projects. We have been to their events and this is truly an amazing organization.

VolunteerMatch
We have always liked their consumer approach. It is an easy site to use and truly the volunteer experts. Their corporate tracking tools and packages are also worth a look for companies wanting to start.