Toad for Oracle has an autocomplete feature.. you type SELECT * FROM USER.
and then press Ctrl+. and a drop down appears where you can choose
This option is under Options -> Editor -> Code Assist. The only time I have ever seen it autofill instead of providing a list is when there is only one table that matches though... What version of Toad are you using?
I had the same problem, it was caused by a corrupt configuration file - try this answer and see if it works.