Perl, 69 74 77 78 79 chars
$a=<>;s:(?{$z=substr$a,$-[0]/4,1})z|#:$z:g,print for`figlet -f3x5 $a`
Sample output:
% echo ABCDEFGHIJKLMNOPQRS | perl banner.pl
A BB CC DD EEE FFF GG H H III JJ K K L M M NNN O PP Q RR SS
A A B B C D D E F G H H I J K K L MMM N N O O P P Q Q R R S
AAA BB C D D EE FF G G HHH I J KK L MMM N N O O PP Q Q RR S
A A B B C D D E F G G H H I J J K K L M M N N O O P QQ R R S
A A BB CC DD EEE F GG H H III J K K LLL M M N N O P Q R R SS
% echo TUVWXYZ \! | perl banner.pl
TTT U U V V W W X X Y Y ZZZ !
T U U V V W W X X Y Y Z !
T U U V V WWW X Y Z !
T U U V V WWW X X Y Z
T UUU V W W X X Y ZZZ !
I assume you have figlet and this figlet font installed on your system. :)
