I just received an email saying Adbeat will be closing from public beta in about 2 weeks, so you should sign up here while it is still free!
What is Adbeat? It lets you see the top PPC ads across the Google Content Network, Yahoo/MSN PPC, DoubleClick, Adsonar, and Pulse360!
You can search out specific advertisers in your niche, and see which adcopies they use the most. You can also search out specific publishers and see which ads appear the most on their sites. You can see which ads appear most on a network by network basis.
It really kicks ass.
Since it is still free, I recommend taking tons of notes on the adcopies used in the markets you compete in! You know, for future reference and stuff 😉 update: the free period is over.
I originally found out about it by watching an interview on Mixergy.com (great site!) with the owner, Mike Colella, entitled The $2.2 Million Affiliate Who Wouldn’t Let Me Interview Him – with Mike Colella