O.K. Lee had some gorgeous cactus pears today at a bargain two for a buck. I've used them for sorbet, and also in margaritas, though I'd imagine they would work in other cocktails, including mojitos. The color of the juice is intense, making any beverage made from it a great showpiece. Four fruits should yield about a cup of juice.
You can find an illustrated guide to peeling and prepping these beauties (not at all hard) here.
Quick thought for another use: make a sugar syrup with it and drizzle atop vanilla ice cream.