Monster.com has the most jobs listed from what I can tell. What I dislike so much about Monster is that everything you do, they force you to another full page (yes/no) advertisement. Also, I wish they would allow you to remain logged in so that every day I wouldn't have to login.

CareerBuilder has the nicest interface of all of the career sites I visit. For some reason, they continue to send me job emails about "chef" jobs... I eat out almost every meal, not sure I am right for being a chef. :)

HotJobs seems to have the lowest number of jobs of the major three job search engines but their lack of intrusive ads, ease of searching make it my overall favorite.