Keep on buying ads like that until you find the right ones, over a few months I was able to find the good sites that had low prices for there ads (far too low, like $5 to $10 a month). Now I get significant traffic for almost no money compared to spending huge sums on Google Adwords. Adbrite is excellent over the long haul.
Also, Adbrite is kind of slow. If they have not approved your ad in one day, that is not unusual. It can take two days often.