Whether we realize it or not, races are a big production. From organizing logistics to distributing numbers and t-shirts, from watching bags to handing out cups, there's a lot that goes into even a 5k. While I obviously love running in races, I feel it's important to give back to the local running community through volunteering.
Another alternative to volunteering for more established groups and larger races is volunteering for small local events. I find that the smaller the event, the more ownership you feel when you volunteer. You also tend to get more interaction with the race organizers and occasionally there are other perks too (free beer, a free future race entry, or even a special volunteer t-shirt). Generally speaking, the people who volunteer at these events tend to be real running enthusiasts. It can be a great opportunity to get to know other local runners, expanding your knowledge of the local running community.
At the very least, by volunteering you gain a new appreciation of the folks who hand you water, distribute race bibs, or time your event. Running may be a largely individual sport but racing takes a village.