it'll be different for everyone; depends what you do and where you are. If you get Vitality - that's my June/July topic.
Essentially though, check your local market and who the local publications reach (research is everything). Ask them for a features list to see if they have something suitable coming up that you can advertise in. Local social groups are worth a shout as are community publications (the local directories that are delivered everywhere).
I am all for the unusual - maybe try adshells (surprisingly cheap), or other unusual mediums. Most importantly though, plan your activity, so that it has a thread and a purpose; unplanned one-offs can be costly and pointless