First - Mezco Heroes Series 3 and 4. Series 1 did well but may have been overstocked. Series 2 disappeared quickly but distribution was lighter. Maybe this was a good thing. I preordered Series 3 and was upset when it was cancelled. Series 4 was also displayed at Toy Fair.
Mezco Heroes - Series 3
Mezco Heroes - Series 4
Another fun set that never made it was McFarlane's Warriors of the Zodiac Series 2.
Series 1 made it to toy shelves. Guess they didn't do well enough.
Finally, while McFarlane Military enjoyed a long run with modern military characters, there were several series of World War II figures planned. I was especially looking forward to the Normandy Beach D-Day, Airborne and Battle of the Bulge figures. They never happened. McFarlane put out the last set branded under the Call of Duty video game which included three Pacific Marines and one winter camouflaged British Commando (kind of an odd selection). The first figure on the top left - charging Marine - was originally painted as a Normandy Beach infantry figure int he tan and beige Europe Theater of Operations (ETO) uniform. The WWII would have provided an awesome array of figures and uniforms, including enemy combatants.
The original World War II series was going to be (and how awesome are these?):
Series 1 - Army Infantry Private (D-Day), Army Infantry BAR Gunner (Battle of the Bulge), Marine Corps Flamethrower (Iwo Jima), and Air Corps P51 Tuskegee Airman along with a Box set of a 30 CAL gunner (Battle of the Bulge).
Series 2 - Army Ranger (D-Day), Navy Boat Gunner's Mate, Army Infantry Grenadier (Monte Cassino) and Army Airborne Captain (Carentan). :-(
What cancelled toy line upsets you the most?