I've always enjoyed Tu Bishvat and everything that it represents. Tu Bishvat is probably the lowest ranked Jewish Holiday and certainly one of the least well known. Tu Bishvat is the New Year for the Trees. This is the season in which the earliest-blooming trees in the Land of Israel emerge from their winter sleep and begin a new fruit-bearing cycle.
Legally, the new year for trees relates to the various tithes that are separated from produce grown in the Holy Land. These tithes differ from year to year in the seven-year shemittah cycle, the point at which a budding fruit is considered to belong to the next year of the cycle is the 15th of Shevat.
As a child my primary memory of Tu Bishvat was eating the Shivat HaMinim - the 7 species special to the land of Israel - wheat, barley, grapes, figs, pomegranates, olives and dates. I loved singing the words from Devarim Chapter 8 Verse 8.
אֶרֶץ חִטָּה וּשְׂעֹרָה, וְגֶפֶן וּתְאֵנָה וְרִמּוֹן; אֶרֶץ-זֵית שֶׁמֶן, וּדְבָשׁ
A land of wheat and barley, and grapes and figs and pomegranates; a land of olive oil and honey (dates).
If you ask me very nicely I won't sing it! The other memory I had was planting trees and sending money to JNF to plant trees in Israel. In the last 100 years Tu Bishvat has been used as both a Zionist day with support for Israel and a day for furthering environmental issues and concerns.
Sephardim, have a much older custom which is to have a Seder Tu Bishvat The custom goes back to the Kabbalists in the 16th Century who worked on a Seder with 4 cups of wine and all the fruits and nuts and highlighting the 7 special fruits of the land of Israel.
In Seattle, we have a slightly different Tu Bishvat seder called Fruticas. Here's the text of the service.