By serving images/files to the client, I assume you mean static files css, js etc.
Most of the time, a simple solution is the best solution. Just host them on a different server under a different subdomin, i.e. http://content.mydomain.com/img/xyz.jpg. You could host them at a data centre on dedicated server giving your perforamace (close to the backbone), you could load balance the url and by have 2+ servers at 2+ different data centers, giving you resilliance and scalability.
You maintence task is then having todo find a replace when promoting your site to live to replace dev/uat content paths with the live content path (tho you'd only need todo this in css files as you could store the paths for content used within aspx files for as config data).