There is a dumpster for electronics in the basement of my apartment block, and I go there regularly to look for stuff.
The only half-interesting keyboard that I have found there though, has been a Key Tronic foam-and-foil keyboard: NKRO but feels horrible.
However, I have snagged many other items from dumpsters. For instance, floor boards and furniture parts that I have built a cabinet and a couple of hanging shelves from. Several picture frames, an IKEA Detolf glass case (for displaying my Star Wars helmet collection) and various pieces of plastic, metal, leather and whatnot that I have recycled for arts and crafts (costuming and props). I did most of this years ago when I was unemployed