The Global Peace Index, which ranks a number of internal and external factors, found Scandinavian countries among the most peaceful, taking the top three spots.   The index, now in its second year, ranks countries according to their relative states of peace, based on factors such as military expenditure and respect for human rights, the homicide rate and other things.

Interesting resourceful blog by  Jimong below.

http://hojupjimong.wordpress.com/2008/05/22/canada-ranked-at-11th-peaceful-country/#comment-3412

Here’s some countries on Global Peace Index Rankings.
Rank         Country
1              Iceland
2              Denmark
3              Norway
.
5              Japan
.
.
11              CANADA
.
.
32              Korea, Republic of
.
36              France
.
.
67              China
.
.
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97             U.S.A.
.
.
133            North Korea
.
139            Somalia
140            IRAQ
FYI, There is more detailed info about how the index is created on their website ( http://www.visionofhumanity.org/gpi/about-gpi/overview.php )  although it’s rather difficult to measure peace by plain data.  Peace might be reflected relatively differently to different culture and situations in my opinion.