I like the code from SpamAssassin, and have borrowed it for many little projects of my own. Just remember, it's GPL, so if you release your program you have to GPL it too - but you are free to use it internally however you like.

(UPDATE:I just noticed it's dual licensed with the Perl Artistic License, so it's "free-er" than I thought...)

See the function start_children in this module. It uses IO::Socket to communicate with each child process.

The reap_children function is also useful.

~Jon