What are the highest paying direct to client per qualified lead types?

Hello all. I have a question. I have been selling leads for about two years. The leads I generate and sell are of a specific niche and I get $300.00 per qualified lead and convert about 30 leads a month strictly using Adwords for traffic. There are some blog posts for SEO and some craigslist posts but most traffic is from Adwords. I drive traffic to one of my websites who's phone number gets forwarded to a call center. If the client chooses to take the lead I get the $300.00. All calls are tracked. This result is extremely consistent based on the money I spend every month on Adwords. I want to be clear that I have been selling leads NOT traffic. I get paid per qualified lead, not per calls or clicks. Let me also say that I spend usually around $900.00 to $1000.00 a month on adwords to achieve my 30 or so leads a month. In other words I spend $1000 and I get a check for $9000 at the end of the month. Because of this type of turn around I am looking to expand my operation. What I am doing now is basically on autopilot and I know I can be making much more money if I start putting some effort into this. I have been putting a plan together to duplicate what I am currently doing but the biggest question I am facing is what type of lead categories are the highest paying right now using my current model. I know what I am doing works so I just want to do the same thing but in different verticals. I am just curios if anyone might be able to break down a list of the highest paying leads when selling direct to a client? I am looking for lead payouts $300.00 and up? Any input is greatly appreciated.