Wow, I have a list of favs that are tied for first:
All shimmery pigments (and clear sky blue)
Zoomlash mascara
Get Surreal Cheekhue
Stiletto l/s (discontinued- and still fuming about it)
Skinfinish Pleasureflush, Gold Deposit, and Pink Porcelain
All Fluidlines
Parrot eyeshadow
Sea Me Shadestick