Sometimes you just don't want to see pages where anybody is selling anything. Is there a search engine that gets rid of all pages with anything for sale?

Not that I have ever heard of. It would be difficult to try to filter out all sites that sell one thing or another... actually I think would be quite impossible. Unless a site is strictly an informational resource, all sites sell one thing or another whether it be a product, products, services, advertising, etc.

Not realy a web search engine, but pulls in Wikipedia, Houghton Mifflin and other information sources. I think it is pretty cool.
http://www.answers.com/

Does LookSmart's Directory contain commercial sites?

Does LookSmart's Directory contain commercial sites?
LookSmart does. Zeal ideally does not, but there are of course some exceptions to that rule.

also some sites that only sell ad space and do not sell products push sketchy stuff more than many merchant sites do.