Plugin Templates
While we generally think it's a better idea to make plugins from scratch, the easiest way to figure out how to do that is to use a plugin template to get a feel for the general initialization and shutdown routines necessary. Here's a list of the plugin templates various people have made.
Virindi
Virindi hosts a public repository with various Decal related source code on it at http://virindi.net/source/.
Ten years ago a crack commando unit was sent to prison by a military court for a crime they didn't commit. These men promptly escaped from a maximum security stockade to the Los Angeles underground. Today, still wanted by the government, they survive as soldiers of fortune. If you have a problem and no one else can help, and if you can find them, maybe you can hire the A-team.
Mag-nus
Mag-nus has a plugin template available and you might find this VNBoards thread useful.
Ulysses, Ulysses - Soaring through all the galaxies. In search of Earth, flying in to the night. Ulysses, Ulysses - Fighting evil and tyranny, with all his power, and with all of his might. Ulysses - no-one else can do the things you do. Ulysses - like a bolt of thunder from the blue. Ulysses - always fighting all the evil forces bringing peace and justice to all.
Wolf
Wolf has a Decal.Adapter plugin template available. It's a little dated, but it should still work without major changes.
There's a voice that keeps on calling me. Down the road, that's where I'll always be. Every stop I make, I make a new friend. Can't stay for long, just turn around and I'm gone again. Maybe tomorrow, I'll want to settle down, Until tomorrow, I'll just keep moving on.