Banner Ads

I have a friend of mine who's wanting to start up an internet magazine, and it seems like (after a while, of course) it'll probably generate a decent amount of traffic. I was wondering if anyone here would happen to know what--if any--would be a good banner ad system to get involved with. I'm sure they don't generate much income unless you're bringing 1K+ hits per day, but I haven't researched this in a long time. Figured this would be a good place to start

www.google.com/adsense
www.tradedoubler.com

Adsense, most definately. It's the one I use.