For ATP events, it is really available only at ATP's site for players - the playerzone.com
Why ATP can't just publish that info at their public site, I don't know. They do charge players some $$$ for an account to use the playerzone website though; perhaps that is one reason. Another is that they don't want people to know who has withdrawn.
I assume that Italian website (I don't think that is the Italian federation's website though) is using info from the playerzone.
For the ATP challengers and ITF satellites in the USA, you can use the USTA website (www.usta.com
) and go to their USTA pro circuits page for the initial entry list and waiting list. They do not update the list as withdrawals come in later (they do it for ITF women's events).
The ITF's wensite http://www.itftennis.com/mens
has the entry lists for the futures and satellite events, posted normally within a couple of days of the close of entries (which is the monday two weeks ahead of the events).