You can change the width of the NAME, TYPE and VALUE of "show parameter" in SQL/Plus.

SQL> show parameter sga

NAME                           TYPE
------------------------------ ------------------------------
VALUE
------------------------------
lock_sga                       boolean
FALSE
pre_page_sga                   boolean
FALSE
sga_max_size                   big integer
300M
sga_target                     big integer
0

SQL> column NAME_COL_PLUS_SHOW_PARAM format A20
SQL> column TYPE format A20
SQL> column VALUE_COL_PLUS_SHOW_PARAM format A20

SQL> show parameter sga

NAME                 TYPE                 VALUE
-------------------- -------------------- --------------------
lock_sga             boolean              FALSE
pre_page_sga         boolean              FALSE
sga_max_size         big integer          300M
sga_target           big integer          0