Mmm, I gotta say this list of pony-based cocktails is quite intriguing. Several of these cocktails are a little silly (and I'm not just talking about the Derpy), but I like the Luna and the Rarity (hmm, quite appropriate, and they're among my favorite MLP:FiM characters to boot):
Rarity — White Cosmopolitan: 1¼ oz vodka, ¾ oz Cointreau, 3 oz white cranberry juice, ½ oz lime juice. Shake well and serve in a martini glass with three blueberries as a garnish.
Luna — Sparkling Blue Cosmo[politan]: 1¼ oz vodka, ¾ oz blue curaçao, ½ oz lime juice. Shake and strain into a martini glass. Top with champagne, garnish with a lime wedge to represent the half moon.
I should find a bar with a skilled bartender who's willing to try new things (seeing as how most bartenders will be unlikely to have heard of pony-based drinks). :)
(Hat tip to EqD, BTW.)