How do I spool to a CSV formatted file using SQLPLUS?

Answer

set colsep ,     -- separate columns with a comma
set pagesize 0   -- No header rows
set trimspool on -- remove trailing blanks
set headsep off  -- this may or may not be useful...depends on your headings.
set linesize X   -- X should be the sum of the column widths
set numw X       -- X should be the length you want for numbers (avoid scientific notation on IDs)

spool myfile.csv

select table_name, tablespace_name
  from all_tables
 where owner = 'SYS'
   and tablespace_name is not null;

Output will be like:

    TABLE_PRIVILEGE_MAP           ,SYSTEM                        
    SYSTEM_PRIVILEGE_MAP          ,SYSTEM                        
    STMT_AUDIT_OPTION_MAP         ,SYSTEM                        
    DUAL                          ,SYSTEM
...