The themes/designs that are currently included with ExpressionEngine are meant to just be a starting point for you.  You can certainly use them as the design for your site if you wish, but the main purpose is simply to give you something to start with; an example that you can look at and disect to see how it works.  By no means are you locked in to using only one of those designs; you’re free to create whatever site design you wish.

There are literally hundreds of websites available that carry designs and themes for sites.  Basically, any of those can be adapted for use in ExpressionEngine; you simply need to bring the design in and then replace the “dynamic” parts of the design with ExpressionEngine tags.

One of our ExpressionEngine users, CharlesG has also created a site dedicated to hosting new EE themes as well as theme and design-related information.

EE Design