This is one of my favorite postage pages for bookmarking/favorites. Good links to all the popular domestic and int'l mail classes. European countries are in Group3 (Group 1 is Canada, Group 2 is Mexico.) On that page there is also a link to that postage calculator mentioned above in this thread -- it is that little red "Go" button near the top of the page. :
http://www.usps.com/prices/welcome.htm

And if you click one of the International mail classes on the page, you get the corresponding chart with a link to all the Group numbers for each country.

Robert