Browser compatibility?

[Encantador]

Hi,

For those with a business website, or perhaps any experts.
What browsers would you want your site to work well on?

Obviously the latest version of Netscape and IE, but what about older versions and other browsers.

I assume no developer will ever claim a site will work well on everything. What should they be offering in terms of browser compatibility if they were quoting to build you a site today?

Thanks in advance.