I was looking for a simple simple Wordpress plugin that just inserted Adsense code randomly into a 
pre-existing blog. All the ones I found would only replace an Adsense comment with Adsense code. That’s great if you want to go through every article you have and post little adsense tags, but for a site that has some bulk to it, it sucks.
It also increased banner blindness by keeping the ads in the same place time after time.
My new Adsense Injection plugin just takes a random paragraph break in your article and inserts adsense code. It does one per story. It lets you pick how many total ads to do (0-3) and it lets you pick the formats and colors you want it to randomly select from. Biggnuts - Adsense Injection