The National Champion jerseys aren't exactly the best looking jerseys out there, and that goes for most of them. Even the World Champion's jersey doesn't really look all that great. The whole idea is to distinguish those riders from the rest of the group.
You've seen the USA Champion's jersey above, here are some others you may have seen at Le Tour de France:
World Champion
Germany
France
Kazakhstan
The Netherlands
Belgium
Norway
Australia
Sweden
Luxembourg
Italy
United Kingdom
I tried to find a good picture of the Spanish jersey, but was unsuccessful.