Pomegranates.

Really really tart (and crisp) green apples.

Some type of pickled veg I had in China last time I was there - often added to noodles. Looks like some kind of tiny chopped green bean.

Lime - fresh lime juice and plain soda, lime wedges, 'real' Key lime pie (hint: if it isn't tart, it isn't 'real', IMHO).