There's a great script called WP Twin.
It allows you to quickly copy and deploy an existing WP installation.
So, all you do is build *one* site, with all your plugins+themes installed and configured. Then make a copy of that site. And with one click, you can deploy that file as a new site on a new domain.
I remember seeing a copy floating around here in the Downloads section.
Alternatively, if all your sites are on one server, you might want to look into using with WordPress MU feature. Basically, it allows you to run several separate and distinct sites/domains, from one set of WordPress files.
Hope that makes sense.