I have been using www.penpalworld.com/ since June, 2009.
I have found many good friends and penpals over there: from the UK, USA, Germany, Poland, Ireland, Canada, Israel, Australia, Austria.
For penpalling with my friends I created a special email address — I use this email only for language exchange with my penpals, in order not to lose any messages because of spam/fishing/any hacker attack/or some nasty subscriptions which I have to clean every day on my regular email addresses.
If you really need to improve your writing skills in any language you like-- English, German, Spanish, Italian, Russian, Chinese, Japanese, Turkish, etc, try this service-- it is user-friendly and has really cheap and cool extra functions like choosing the country you like for penpalling, choosing a penpal of definite age, with photo or without, with nickname or without, etc.
What's good about this service: you can find a person who has the same or similar hobbies, interests, education level, preferences or the mindset you like.