Are you asking what Google AdSense ad formats tend to get more advertisers? If so, the larger ones generally do better. Here are some examples. 336x280 large rectangle 300x250 inline rectangle 160x600 wide skyscraper Now, if you are asking what keywords have the highest CPC you are going to have to do some homework. Start with the most competitive industries and you should find plenty. I saw a post floating around here the other day where people were listing the most competitive niches they found. Use the Google keyword tool to get cost estimates.
Also you can use broad keywords like: Loans Insurance Homes take broad term of the industry you are looking at and than go to the Google keyword tool and Choose data to display for cost and position estimates... that will help...
There is actually some effort involved here so to be quite frank most are not going to just post the results for niches they have identified as higher paying items. That being said the Google keyword tool is an excellent starting point and will get you what you need. Good luck!