If you are on Solaris (10 or higher works from experience) you can grant a single user the ability to bind to the lower ports:

  usermod -K defaultpriv=basic,net_privaddr ${user}

You can off course also assign the privileges to a role, and then assign the user that role so as required they can su to the role and use the privileges.

Here is a pretty neat description of what is possible and why it is pretty awesome: http://www.c0t0d0s0.org/archives/4075-Less-known-Solaris-fea...

---

On FreeBSD if you have the MAC framework enabled, you can use the portacl module to give new privileges:

  sysctl security.mac.portacl.rules=uid:$user_id:tcp:80

See http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/ma... for more information.