Which browser
 

Which common browsers and version should I check a new site with to make sure of overall compatibility?

IE5.5+
NS4x
NS6 & NS7

Check in all 4 of these browsers, as the different versions of NS, render the page differently. NS7 does a great job of mimicking IE, however, NS6 breaks in some cases, where NS4 and NS7 do not. :)

As you also know, NS4x will also break where other versions will not. My suggestion, is to refrain from using any DHTML in your pages, and try to stick to static only, if you are wanting to have good cross browser compatibility.

My :2 cents: