I usually check for high Adsense paying keywords on rumbler.com.

They have a huge list (2,600 keywords), listed in alphabetical order.

Here's the link: http://www.rumler.com/google/adsense/top-paying-keywords.php

(it's not my site)

For some time now, the highest paying keywords are about lawyers, bad credit, debt consolidation, mesothelioma, life insurance...

letter - keyword - average cpc

A - adverse credit remortgage - 31,10

B - benchmark lending - 40,36

C - ca lemon law - 36,55

D - domains yahoo - 97,44

E - event management security - 24,30

F - federal criminal defense attorney - 23,09

G - google affiliate - 27,11

H - hair removal washington dc - 51,14

I - insurance medical temporary - 29,10

J - jumbo mortgage super - 8,34

K - kanzas home equity loan - 8,64

L - law lemon wisconsin - 66,15

M - mesothelioma information - 30,78

N - new york personal injury lawyer - 19,99

O - orlando criminal attorney - 24,15

P - peritoneal mesothelioma - 36,59

Q - quote remortgage - 6,75

R - refinance with bad credit - 22,61

S - symptoms of mesothelioma - 21,33

T - term life insurance - 20,49

U - uk homeowner loans - 23,78

V - vioxx lawsuit - 23,71

W - www eloan com - 14,99

Y - yahoo web hosting - 37,86

Z - zero apr credit card - 7,83

Personally, I don't make websites about any of these high paying keywords. It is very difficult to rank well in search engines, since your competition is huge. Many sites in those niches exist for years and have thousands of backlinks already.

I rather spend my time working with smaller, less popular niches where I can expect decent rankings much sooner.

But it's always tempting!