If you're going to volunteer, go find an non profit that speaks to you and volunteer there. At least if you don't get a job lead out of it you'll feel good about the work you did instead of bitter over doing free labour for a company that didn't give you a job in the end.
In my personal case, I did volunteer work for an non-profit ISP just starting up way up north. 6 months later, I was being paid for the same work, and jump started my professional career.
There are options for lots of types of geeks, from the "we recycle used computers for disadvantaged people" to the "We send you to an impoverished country to bootstrap their technology base" ones.
I believe the ICRC is always looking for skilled technical people who can think outside the box too.
I enjoyed my time doing non profit work immensely and it still comes up 15 yrs later in job interviews, as some of my best war stories come from those jobs. There's something about the combination of the startup shoestring budget and the feeling that you're actually improving the world that comes together and energizes me. Your mileage may of course very.