A-ads is as good as it gets, to be honest. You could try for cheaper like Mellow, but you're going to get blasted mainly on faucet sites (if that's your target then that's fine too. Kickasstraffic and the like are surf types, you never know as the audience actually does enjoy marketing.

If you *do* like faucet audiences, freebitco.in and moonbitco.in are as good as it gets.

I would really recommend the forum advertising or signature campaigns for more organic reach though as suggested above... though again, if you're looking for marketing audiences, you're probably better off giving it away free with one of them signal groups. Advice: pay in Bitcoin or your results won't be worth it.

Long-term reach? Write a news article about it with really original content and submit it as a story to all the news sites. Then you got backlinks from all these places for SEO.