In the order in which they were written:

Count Electric Sheep 'til You Dream of Me : Taoris. Just general fluff, really explains nothing about the universe but a lot about Kris and his relationship with Tao.

There's No Place Like Home : Kaisoo. Explains how Kai became a part of the team and what his background is. 

A Little Less 16 Candles A Little More Touch Me : Minseok/Yixing ; eventual Lu Han/Minseok/Yixing. The previous stories mention that something is up with Yixing, this explains what that is.

Are You There, God? : How Sehun joined the team and what happened to him.

Love on My Lips : Taoris bonding over language.

Truly Madly Deeply : Kaisoo. Kyungsoo and Kai enjoy a swim in the ocean.

Where There's Smoke : Chanyeol's not all that great at controling his fire power

If I Ain't Got You : Baekhyun kind of wants to kill Jongdae, and also kind of wants to kiss him.

Mission Impossible : The Agents go on a mission (finally)

Love You to Death : Kris learns that his father is dying and goes home to say goodbye

Make the Fireflies Dance : Sehun and Suho discuss The Kiss

With Love : A series of one shots about the couples

My Heart Will Go On : The final(?) adventure, in which nothing will be the same again.

(If you wanted to read them in order in which they happen in canon, it would be No Place Like Home, Electric Sheep, 16 candles, Are You There God, If I Ain't Got You, Where There's Smoke, Truly Madly Deeply, Love on My Lips, Mission Impossible, Make the Fireflies Dance, Love You to Death, With Love).

And there's an offshot of the adventures of the team's puppy, Hero, written by ChiaToma here