Task: Easily pick volunteer opportunities
Effort level: Depends
So NY cares is for the NY area (I will write a post soon with more global sites) and was mentioned in the Volunteer Spotlight by Jayant. Very easy site that allows one to choose projects based on one's interest, location, and availability.
For example,did you know that NEARLY HALF of homeless shelter residents are CHILDREN? Using NY cares you can help enrich their lives by reading a bedtime story, teaching them math and/or computer skills or organize a sports game (among other things). Other projects target adults, meals, health care, environment, etc. Some require a commitment of few months but there are many that require just a couple hours. We are currently using this site to organise student groups to take part in some of these activities.