Most of the coding I do is small projects made for specific jobs - data processing, simulations, tools to make every day life easier, etc. But I do have (or have had) some projects that might be useful/amusing for other people as well:
SDL Tunneler - A clone of legendary DOS-game.
PIC Burner - The ultimate PIC programmer.
IBSimu - An ion beam simulation library.
SuiteSparse - A redistribution of SuiteSparse
sparse matrix library by Tim Davis.