For mangas, the
English wiki has a nice description, and the
Japanese wiki has a good list.
The most notable ones:
the main adaptations that follow pretty closely to the original game story: "Little Busters!" (Anagura Mogura) for LB, and "Little Busters! Ecstasy" (ZEN) for LBEX;
and the main 4komas: "Little Busters! The 4koma" and "Little Busters! EX The 4koma" (Sasagiri Yuuya).
For novels/short stories, there were short stories published with each chapter of the 4koma dengekiG. These follows the game story closely.
There's also LB SSS (Shuffle Short Stories), a collection of random short stories by various writers using LB's characters and setting.
The short story portrayed in the ED is from LB's Perfect Visual Book.
Wiki lists others, but I don't have those.
For radio, Natsume Brothers started in 2008, with hosts Tamiyasu (Rin) and Midorikawa (Kyousuke). Suzuta (Kud) joined the show and it was renamed to Natsume Brothers (21), for obvious reasons.
The whole radio series ran for 171 sessions, not counting the special they released with LB Converted Edition and radio CD specials, and ended last Oct. One of the most entertaining radio shows I've listened to.
Now it starts again as Little Busters! R, with the same hosts, but Tamiyasu's name is written differently, and Suzuta is now Wakabayashi, a fact they seem to openly ignore, but the show's atmosphere seems to be the same as before.