What are some volunteer suggestions for the Bay Area?

I don't know anything about volunteering in the Bay Area, but I have done some work in volunteer placement in other cities.  Based on your irregular availability, I suspect that the best thing that you could do would be environmental work.  Working with a local wildlife service to remove trash and invasive species from protected areas is a really great way to spend a few hours.  It's refreshing physically and usually you meet a really interesting group of folks while you work. If you are more interested in working with disadvantaged people, you probably need to be willing to commit to a somewhat more regular schedule.  A lot of work in things like mentoring, tutoring or elderly care tends to require building strong personal relationships, which is difficult if you cannot make a regular time commitment.

I would recommend Habitat for Humanity which often has weekend building events with no prior experience or full time commitment necessary.  Habitat 4 Humanity is a well-run organization, where you know the beneficiaries are both appreciative and deserving, plus you gain hands-on practical skills like how to install towel racks in bathrooms, stain and paint,  repair drywall, or tile the kitchen.  There are also professionals working alongside you who will help you out, so you'll gain some knowledge as well.  In college many of us would spend our spring breaks volunteering in random cities, while meeting other volunteers and learning some useful life skills. The best part is when you work side-by-side with the families who are required by the program to add 'sweat equity' in exchange for the significantly discounted house. There are weekend events as well, which you can find out about through the email list (http://habitatgsf.org/).  I would also recommend checking out the websites of Red Cross/Crescent, Salvation Army, and other community groups.

Formal organizations like those mentioned above can certainly use your assistance ad-hoc if you just let them know your situation.  However, if you have a little time, have you considered just being a better neighbor where ever you are?  Nobody says volunteering has to be "formal."  Sure, we've encouraged high school kids to have more formal volunteer activities in place--it looks good for the college applications and so forth.  But the reality is that there are opportunities all around us every day to do a good deed/volunteer.  Just look around you and see what needs exist in your own immediate vicinity.   For example, are there people in your own community that could use a little extra help? Do you have senior citizen neighbors who could use help from time-to-time with little projects around the house or just who would like another younger friend around?  Do you live near an assisted living or nursing care facility where you could stop in and play a bit of scrabble with the elderly located there? I used to stop by a local nursing home on my way home from work and I'd play the piano in their recreation room when I had a minute.  I also used to play a hand of cards and just talk to the lonely folks there.  I put it in my schedule to do this at least twice a month.  Casual, it worked for me and them. Similarly, you may have other neighbors, friends, or coworkers who could use a little help from time-to-time.  Help them with researching purchasing decisions, talk to their high school age kids about your work and school experiences, help someone with a hobby project.  Be casually available to give someone--young, new to the area, on a budget-- a ride to pick up their car at the shop or drop them off at the airport.  I just helped someone design a logo for a kid's baseball team.  Do I have kids, no.  I just had a skill that could help someone out. If you consider your opportunities to just help your neighbors, you might find all your spare time full of rewarding activity. If we ALL were actively engaged in helping the people around us when they need it, there'd be a lot more time for all of us to also work together to meet the needs of others outside of our immediate sphere.

You might want to check out http://CreateTheGood.org. The website lets you search for local volunteer opportunities by zip code and keyword. But what is nice about it, is if you register with your email address, they will send you an email every couple of weeks that list all of the new volunteer opportunities in you area. So it's really easy to see what's new. Has anyone else on here tried this site before?

Check out Hands on Bay Area.. it's designed to solve just the problem you're facing -  You can select projects you want to volunteer for on an Ad-hoc basis http://www.handsonbayarea.org/