Above all keep it simple and clean. Spend 4-5 hours visiting every website you can think of and note those that are easiest to read and where information can be quickly/easily found. Avoid clutter. Limit how much goes on a page. Keep the font sizes large.
I use a high res UXGA monitor (1200x1600 dpi) because I view a PC display 6-8 hours a day and don't want to get eye strain. So that everything does not display in tiny sizes with this high res setting, I set WinXP's dpi setting to 200%. Now everything appears in a large SVGA (600x800dpi) size.
This setup works perfectly with the letsrun website. Everything appears crystal sharp and everything appears where the page designer wanted it to appear. But amazingly the websites of most major corporations do not display very well using 1200x1600 UXGA along with a 200%dpi setting. Keep doing whatever you are doing to insure that your webpages display nicely on monitors using both low, medium and very high display resolutions.
The dyestat website that others recommended is not terrible, but it is not very good either. It displays much worse on my monitor (print far too small) than does letsrun. Readability is key. Not all your runners have 20/20 vision.
UPS.com and RottenTomatoes.com recently redesigned their websites. They did such a bad job that I can't even go to their websites if my monitor is set to high resolution & 200% dpi. So be sure you test what you change before you release it.