Omitting [INTO] in the INSERT ... SELECT statement
Check out the correct answer to this question - and Bill Karwin's comment on that answer. I was quite surprised to learn that INTO was optional - but indeed it is, although according to the standard it shouldn't be. Amazingly enough, Oracle does require it - must be the only time that Oracle actually enforces one of the ANSI standards where (many*) others leave it optional!

(*) Sybase, MS SQL Server and MySQL amongst others. IBM DB2, Firebird and PostgreSQL seem to enforce the standard.