perltidy will do HTML syntax highlighting for Perl. For SQL you could just use SQL::Parser or maybe SQL::Statement to do the parsing and add color as you see fit. Personally I think:

SELECT id 
FROM address_book
WHERE username = ? 
OR private_address IS NULL
[download]

is pretty enough already.

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

if by 'pretty print' you mean 'colorize', while not Perl Vim does good by me for the coloring part. i even think i remember seeing a macro or example in the distribution for colorizing from the shell.

but if you want to start writing a module here's what Vim uses as it's guideline, it shouldn't be to hard to check for the special words and wrap them with some color.

What operating system did you want a program for? For windows there is a program in VB which keeps track off all the variables and highlights them along with loop and if statements. To find it just type perl in search in the Visual basic part at http://www.planet-source-code.com