Well going from the Collections section, here are what have been mini's:
2003: Pigments, Lipglass, Lipglass Stain
2004: Lipglass, Lipglass Tasti, Pigment, Paint, nail lacquer
2005: Paints, Pigments, Lipgelee, Shadesticks, Lip/Lustreglass (warm and cool)
2006: Shadesticks, Pigments (warm and cool), Lipgelee, Lip/Lustreglass (warm and cool)
2007: Lip/Lustreglass, Softsparkle, Pigments, Plushglass
I definitely think a little nail lacquer set would be really cute, and really giftable. Also maybe a similar concept to the Softsparkle, in having a few different liners. Maybe have Feline, Minted, Stubborn Brown, Orpheus, and Blooz. Also for pigments, I would love instead of warm or cool, how about Neutral, Brights, and Glitters. Maybe a Reflects glitter set.