Tu B'Shvat at Torah.org
Classes and articles.
http://www.torah.org/learning/yomtov/tubshvat/

Tu B'Shvat at Ohr Somayach
Essays, articles and poetry.
http://www.ohr.org.il/yhiy.php/holidays/tu_bshvat/

Judaism 101: Tu B'Shevat
Discusses the holiday of Tu B'Shevat, the Jewish New Year for Trees.
http://www.jewfaq.org/holiday8.htm

Tu B'Shvat with Akhlah
Traditions, crafts, vocabulary and Seder. For children.
http://www.akhlah.com/holidays/tubshvat/tu_bshvat.php

Tu B'Shevat at Chabad.org
Collection of related essays.
http://www.chabad.org/library/article.asp?AID=3264