We used some of those plastic Cajun Classic meat injectors (image on right) to inject our birds (ducks, turkeys, pheasants, etc): Deep Fry Turkey Day with Red-neck Yankees, aka Les Tres Riche Heures du Bird Dog.
Those plastic injectors are worthless crap. The herbs and spices jam up the injector holes, and the whole thing falls apart after a few birds.
We then made do with a large-apertured medical syringe which one of our medical friends had (which I hope was clean), but this is really the cooking tool that is needed: the stainless steel Bayou Classic with one needle for herb mixtures and another for marinade (photo below).
Many folks like to inject a turkey with sherry or cider.
I bought a couple of those for my cooking buddies. (Update: I did, and got one for myself too. Would be scary to see a nurse approaching you with one of these.)
This year, I am going to inject those big SOBs with a warmed mix of sherry, butter, honey, and herbs under the skin and deep into the meat. That can not be bad. The Indians did it that way, didn't they? Of course they did - when they weren't busy scalping, raping, and torturing their neighboring tribes.