Just came across a pretty interesting and entertaining look at three advertising channels that one can use to monetize their websites, including a look at demographics and such. For example, this look at Federated Media and MSN AdCenter:

MSN Advertising says MSN Tech & Gadgets (MSN and partner content) is “the place to reach technology users”:

Demographics
Gender: 70% male, 30% female
Age: 69% are 25-54
Income: 61% have household income $50K+, 41% have household income $75K+
Education: 50% college graduates or higher
Occupation: 42% are professional/managerial

Federated Media says its sites “cater to cultural influencers, technology decision makers, early adopters…”:

Demographics
Gender: 79% male
Average Age: 32.7
Income: Average household income range $50,000-$74,999
Occupation: 50% management, 20% Director or above

It should be noted that Federated Media is a closed advertising network, but the benefit there is that if you fit into their network, you stand to see a nice increase in revenue.