1. Adult content 2. Too many AdSense for content units (4 instead of 3 max) 3. Keyword loaded 4. META tags stacked I think that's about it. To be honest #4 isn't specifically against AdSense TOS, but is contrary to the G webmaster guidelines.
*EDIT* Oops, I took too long to browse around so loads of people have posted already. Also I didn't notice the one about the META tags. =============== OMG - that is ridiculous!!! I found the following, is there more? 4 Content Units, whereas only 3 allowed per page Trying to force unrelated ads (student loans consolidation) Porn site <Reporting...>
Look how the title matches the sites content: Student Loan Consolidation! Someone is about to loose his/here adsense account :d