I heard good things about purchasing solo ads and I've had pretty good conversions with microsoft adcenter although it's a bit pricey. I guess after you build your list to a decent level it'd be a good idea to do traffic exchanges with other list owners.
What do you guys think about the above strategies and do you know cheap sources of traffic that convert well? Other than google adwords and microsoft adcenter what the other PPC sources are with decent conversions. Facebook ads, POF?