I talk about pen pal friendships a lot here. It's always nice to find new friends, and pen pals can occasionally be transformed into real life friends. However, use caution when finding pen pals. Use a double blind mail system or P.O. Box when first corresponding. Don't give out information that could put you in jeopardy.
The best ways to find pen pals is through a reputable source, like your school or through a social activity that is monitored closely.
I've come across a few websites that connect pen pals, however use caution with these. Read the information carefully and note that I have not used these myself. If any of you have experience with these sites, please let me know.