Secure Port Testing

Hello List,

I am responsible for testing connectivity between customers and vendor
sites and often need to verify and test firewall settings for extranet
connections before the data link is available.  In the past I would
just set up a test box on a test LAN on the external interface of the
Firewall and pick a service and run it on  whatever port I need to
test. I am looking for something more secure and configurable that
wont put an actual service out in the open.  Hopefully a tool that
will allow me to open ports on a windows / or *nix box without
actually having a particular service running there.  Maybe a banner,
or just something that will allow me to determine if the connection
was successful.  Preferably I would like the ability to open multiple
ports at a time and be able to make quick to changes.  My methodology
is that if I get a positive connection I know the firewall is allowing
me through and routing properly.

Any recommendations for tools or different perspectives on how to test
this will be greatly appreciated!

Thanks.