Career Help and Advice

Does Google post their jobs on CareerBuilder, or AT&T, or other major companies? Not that I would apply at these companies, specifically, but I wonder if it best just to apply to the jobs that interest you directly? Wouldn't a better approach be to find a company you want to work for and pursue it? These sites frustrate me because most the postings are made by staffing agencies, which have problems too numerous to list here. The rest of the postings are for jobs that are difficult to fill for whatever reason like ridiculous requirements. But the problem with applying for jobs directly is, I am not aware of every company in my area and the process seems to take forever.