Last year, our group did a monthly dinner for the Rainbow House (it's like Ronald McDonald House) at the Children's Hospital here. This meant providing a meal for 30 people. We had a lot of fun planning, shopping and preparing the dinners. We also did Easter baskets for them with all kinds of toiletries, snacks, etc. The director told us that some of the families staying there were flown in on an emergency basis and had NO personal supplies, so they were really excited to get them.
We also did a school supply drive for a local charity in August.
One idea we found out about is that our local Make a Wish program needs people to help make scrapbooks for participants. If anyone in your group is into scrapping, this could be a really fun activity that they'd really appreciate. I thought it was really neat that they made these special memory books of those trips for the kids.
Personally - I volunteer at the library teaching beginning computer classes. Anyone can sign up, but it's mostly senior citizens and I just cover really basic things like e-mail, using the internet, etc. You wouldn't need to be a computer expert to teach these classes (I'm not, but I'm tech-savvy enough to answer the questions they have).