I have a site related to law, attorneys, and other legal resources. I have adsense contextual ads on several pages, embedded within content but easily identifiable as ads. There are four books at amazon.com that are highly related to the topic of my site and I think the visitors to my site might find them very useful. I am thinking of promoting the books on the left sidebar. The formatting is Amazon Widgets and they look very different from adsense contexual ads.
Is this allowed? Adsense TOS doesn't specifically address this. Maybe I misunderstood, but I heard sites promoting affiliate products are not accepted.