Don't hardcode OAM addresses - Pretty much what it says on the tin.
Watermarking - How to watermark an ASM program (can be applied to C, but not as easily)
GBC dual compatibility - When a GBC-only game is reasonable, and when it's an excuse
Paper by Belial - Quick description of the Game Boy hardware and GBDK programming
Struct - A discussion of what structs are, how to use them, and how to efficiently manipulate them.
Unfinished tutorial by Duo: ASMSchool
RGBDS Super Game Boy tutorial Works on the implementation of Super Game Boy functionalities in an existing template program.
GBDK Sprite Tutorial An exhaustive explanation of basic sprite functions in GBDK, building up from fundamentals
GBDK Joypad Tutorial Using the joypad and associated functions to check button input
Originally from Gameboy Dev'rs, links since broken.
ZGB Installation Tutorial A game engine for the Game Boy