Montenegro springs to mind, which gained independence from Serbia through a referendum in 2006. However, this breaks the 20 year rule on this subreddit so I won't go into too much detail about it.

One independence I can talk about is the dissolution of Czechoslovakia in 1992/3, which is sometimes referred to as the 'Velvet Divorce' which refers to the peaceful 'Velvet Revolution' in 1989 which led to to fall of the Communist party. On the 17th July 1992, Slovakia declared its independence from the Czechoslovakia, which was dissolved 6 days later. It was a peaceful division, and some would argue an inevitable one, due to the stark differences between the Czech and Slovak people.

Most British colonies, e.g. Australia, Canada, South Africa and New Zealand also all achieved independence peacefully through the 20th century. Portugal's colony of Brazil also achieved independence with almost full peace (there was some guerilla fighting between Portuguese troops and citizens) in 1822.