Overview

Aish Hatorah
http://aish.com/holidays/Tu_BShvat/holiday_page.asp

Ahavat Israel
http://www.ahavat-israel.com/torat/tubishvat.html

Gates of Jewish Heritage
http://www.jewishgates.org/taland/talmud/calendar/tu.stm

JEWFAQ
http://www.jewfaq.org/holiday8.htm

JAFI - Pedagogic Center
http://www.jajz-ed.org.il/festivls/tubish/index.html

KKL-JNF
Four short articles about the sources and celebration of Tu B'Shvat, then and now, with source texts.
http://www.kkl.org.il/kkl/english/main_subject/events_and_trips/pearls.x

WUJS
http://www.wujs.org.il/activist/tu_bshvat/index.shtml

UAHC
http://uahc.org/congs/ma/ma002/tubishvat.html

International Competition on Jewish Identity
http://www.biu.ac.il/ICJI/Competition/chapter7/724.htm

Advanced

Ohr Samayach
http://www.ohr.org.il/special/tubshvat/

Project Genesis (Torah Org)
http://torah.org/learning/yomtov/tubshvat/