Also depends on the age and situations of your singles. Are they single, never married, no kids? What age? Are they divorcees? With kids? Widowed? For people with kids, do some activities where kids can participate, because otherwise it's hard for some people to get to events. So sometimes go to a park or provide free sitting during the event.
Skating, minigolf, bumper boats, go-carts, hiking trips, skee shoot, paintball... trust me, with most singles things, if you can get the guys there, even if its a "guy" type event for the most part, the ladies will be there.

But if you do a "girl" thing, the guys will find something more interesting to do. Try paintball combined with a restaurant... let anyone who doesn't want to do paintball to meet you at a specified time after you finish so that everyone can eat together. That way you can get a feel for what people want to do. Mix it up some, everyone can enjoy the boats or go-carts or a concert, movie, or dinner out. You could do a museum trip, camping, canoeing, horseback riding, hayride, corn maze... try checking
www.roadsideamerica.com for some weird things to do locally. Depending on the group, they might also be interested in volunteering for Habitat for Humanity or some other group one day, or helping elderly people in the neighborhood...
Watch the prices, since most singles are a little short of money.
You might also find out if they would be interested in a one night class on balancing church and life, a career seminar, or money management.
The most important things probably involve your interaction with them, more than the activities you do. Respect them as individuals, blessed in a unique way. NOT un-blessed because they are single. Believe me, I will NOT be part of a group that says "oh, honey, don't worry about it. Someday you'll be blessed with a family too, if you just live for God. After all, God will supply all our needs." There is so much wrong with that statement, I won't start. One other thing I would NEVER recommend doing... please don't tell any of them that you just can't relate because you've always been married or got married so young. And try to stay out of the dating thing... singles already have the concept of singles meetings as a cover for matchmaking/dating figured out. Try to break out of that concept and just all have fun.