I have a large site which doesn't have any more than a '404 Page Not Found' message for bad page names. AdSense has worked best on my content pages, but I'm wondering what ad products work best on 404 pages.
two things to keep in mind: a) when the visitor gets a 404 error page, he was either misdirected there by an unvalid link because you changed the structure of your site. For real visitors (humans) you should offer something based on the requested url. maybe it contains a product name so you can provide a link to a product or category. Also a site search and a link to the site map can be helpful. b) analyze where the 404s are coming from - I have a small php script on my 404 page that tracks the referring url so I can go in and fix broken links. It is sometimes difficult to fix things when an external site has a misspelled link to your page, but you can then either do redirects or setup a page with exactly that name.
isn't it against adsense rules to have adsense blocks on 404pages?
It seems not to be dataguys intention to put AS there