Something I've also wrestled with... and since my designs tend to be heavy on
the graphic design side, here are a couple of ways I've dealt with it...
take a look:

Hawaii Healing Ohana - For the Healing of Your Life ... (center justified.. plenty of negative space ok, and it also displays well on smaller/squarer monitors)

Garden Island Granite - Lihue, Kauai (left justified - in process, but you can see the extended background to avoid big white spaces on the right side...)

About Kenneth Lee, Realtor Broker, www.kennethleehawaii.com (left justified, top and bottom of page's grapics extend 100% across browser window)

I have increased the width of my pages in recent years from a standard size of 850 to 950 or 1050, to accommodate the wider format screens as well, but for those with 'standard' resolutions, going much wider than that makes the layout look too 'big'.

The fluid design technique works great for sites that are mostly text, with a few images, but for graphic design sites, it's problematic, and difficult to keep the same look across all browsers and monitors...

- Puamana