Scrbd and issuu. I will not claim that these are the best but these are what I use. I think 4shared is still pretty decent though.
You could use issuu for free so as 4shared. Depositfiles and uploaded.to are also free. The list goes on and on. You have to be more specific on what you are looking for because almost all of these sites offer the same services.
You can share your pdf on Slideshare. This is the best PDF/PPT sharing website which helps in SERP ranking.