i think make query with auto approve in search engine. by that you can get relavant search results. like if you want auto blog comments approve site, you can simply search "auto approve blog commenting site list".
Using auto approval sites for off page SEO activities is not good in term of google as those sites doesnot have good PR, content and mostly sites are used for spamming. So builing links on such sites will create bad neighbourhood for your websites. Better to search high PR quality and Theme based sites for builing links.
Now a days a build backlink Backlink is a big factor for search ranking & targeted visitor. Blog comment is the Most popular backlink method. But there is a problem due to spam major popular & high PR blog owner are disable the auto approve system beside they use anti spam plugin which automatically delete comment.