Special Interest Pen Pals

Balloonfriend.com - Supplies and releases a balloon containing the site's details, in the hopes that the finder will reply and establish pen pal contact. Also offers friend matching and dating services. United Kingdom.
Handicapped Friends Pen Pal Club - A nonprofit pen pal service for the disabled and anyone else interested. Publishes a quarterly newsletter. Membership fee charged.
Ladies Only Pen Pals - A penpal site for women over the age of 18.
Meet a Soldier Online - Meet single soldiers and other military personnel.
Student Letter Exchange - Matches students with other students wanting penpals, ages 9-18.
Victorian Friends - A site for people who love the Victorian era. Sign or view the guest book to find pen pals.
World Pen Pals - Fee based service for students to write to other students. Includes application forms for teachers and group leaders.
forcespenpals.co.uk - Penpals, social networking and dating for the UK armed forces, supporting soldiers deployed in Afghanistan, Iraq and elsewhere. Includes news and success stories.