On small tables, the simplest / easiest to remember way:
select rowid
from table_name a
where rowid >
(select min(rowid) from table_name b
where a.col1 = b.col1
and a.col2 = b.col2
and a.col3 = b.col3
etc..
);
The most efficient is probably using rank() or row_number().
More on rank():
http://www.pythian.com/news/209/oracle-deleting-duplicate-rows-efficiently/
More on row_number():
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:15258974323143
http://download.oracle.com/docs/cd/B14117_01/server.101/b10759/functions122.htm
