Whenever I lecture about trends in TV, the first thing I note is that there's one surefire way to explain even the strangest moves you might see in the industry:

By looking at the dollar signs.

So it made sense when Forbes.com turned to analysts TNS Media Intelligence to grab the advertising fees for the top shows on television -- figures mostly based on the early ad buying season called the upfronts, which start in May.

Small surprise, American Idol was at the top, earning $7-million every 30 minutes as the highest-rated show on network TV. The numbers prove that there's still bucketloads of money pouring into the broadcast shows which can still draw an audience, especially a young one.

And, of course, four of the 10 highest earning shows are unscripted "reality TV" programs. (another big surprise; fourth-place NBC has just one show on this list, the seriously ailing Heroes)

Still, Forbes' list offers an eye-opening window into the money still flying around TV's dream factory. No wonder Fox keeps kissing up to Simon Cowell -- what else in a slumping, modern-day media could earn $623,000 in 30 seconds?

1) American Idol  (Fox)
Revenue per 30 minutes: $7 million
Average cost of a 30-second ad: $623,000
Viewers*: 25.6 million

 2) 24 (Fox)
Revenue per 30 minutes: $3.7 million
Average cost of a 30-second ad: $366,000
Viewers: 11.7 million

3) Desperate Housewives (ABC)
Revenue per 30 minutes: $2.9 million
Average cost of a 30-second ad: $251,000
Viewers: 15.2 million

4) Grey's Anatomy (ABC)
Revenue per 30 minutes: $2.7 million
Average cost of a 30-second ad: $224,000
Viewers: 13.4 million

5) Two and a Half Men (CBS)
Revenue per 30 minutes: $2.6 million
Average cost of a 30-second ad: $227,000
Viewers: 14.1 million

6) Dancing With the Stars: Results (ABC)
Revenue per 30 minutes: $2.5 million
Average cost of a 30-second ad: $205,000
Viewers: 16.8 million

7) Dancing With the Stars (ABC)
Revenue per 30 minutes: $2.4 million
Average cost of a 30-second ad: $196,000
Viewers: 19.8 million

 8) Heroes (NBC)
Revenue per 30 minutes: $2.1 million
Average cost of a 30-second ad: $194,000
Viewers: 7.9 million

9) Brothers and Sisters (ABC)
Revenue per 30 minutes: $2.1 million
Average cost of a 30-second ad: $195,000
Viewers: 10.1 million

10) Survivor: Gabon (CBS)
Revenue per 30 minutes: $2.1 million
Average cost of a 30-sec ad: $204,000
Viewers: 12.9 million