The best configuration for Webmasters...

Depends on what your tasks entail... and how much cash you have.

I personally run one mac with two 30" monitors and one PC with two 30" monitors as well as a mac laptop. I run synergy to give me single mouse and single keyboard access across all machines. I also run a linux machine separate that I use for local development and cross browser testing. I use a Buffalo TeraStation Pro (6TB Raid 5) for content storage and backups...

I'm a developer, designer, and (I suppose) "webmaster".

I have a big desk :P