Fruits of the Incas
I came across a great book a while back, and amazingly it turns out that its available free online: Lost Crops of the Incas: Little Known Plants of the Andes with Promise for Worldwide Cultivation, from National Academies Press. It's an amzingly thorough overview of just about every imaginable endemic crop of the Andes (every one I could imagine, actually, and then some). You can read it online for free, or you can buy the PDF (or, if you're really cheap and/or bored, you can print each of the single page JPEGs individually).
While European colonists adopted many native crops in their expansion over the globe, to a remarkably large extent imported crops replaced the indigenous, despite in many cases being poorly adapted to the local conditions. There are probably as many reasons for this as there are crops, not least among them being that when your colonial overlords tell you to grow something different, you probably do (at least where they're watching).
Ultimately, the Spanish and the rest of the world saw the advantages of many of the Andean vegetables (potatoes, peppers, tomatoes and beans being the most obvious examples). The fruits, however, have remained in relative obscurity. While many continue as staples of local markets and widely consumed among indigenous populations, very few have made a significant impact on the world fruit industry. I'm hardly qualified to comment on the exact reasons for this, but part of it probably is the result of their adaptation to a very unusual set of climatic conditions. The Andes combine being smack-dab on the equator with extremely high altitude, so the plants tend to have an extremely low chilling requirement combined with a sensitivity to extremes of both heat and cold. This particular sort of adaptation might also limit geographic expansion of the crops' ranges, because movement east or west (ie, out of the mountains) results in a significant change in climate due to altitude, while movement north or south changes conditions due to latitude. (Jared Diamond, in his excellent Guns, Germs and Steel, theorizes that the east-west axis of Eurasia facilitated the spread of crop species, while the north-south arrangement of the Americas discouraged it.)
Whatever the reason, it's really too bad more of them haven't made it to our grocery stores. In addition to the cherimoya, and bunch of indigenous relatives of things like blackberries and blueberries, there are dozens of other species waiting to be discovered by world markets. And now, thanks to the wonder that is the global shipping infrastructure (which I must admit to having blamed for the decline of many crops in the past), there's no immediate need for these crops to be grown outside of their narrow range, though many are, and with a little breeding effort many more probably could be.
A few are beginning to find both markets and production areas outside of the region. The ugni (Myrtus ugni or Ugni molinae, depending on which authority you believe) has been found well-adapted to the moderate climates of New Zealand and Tasmania, both of which have found more market-friendly names for it ("New Zealand Cranberry" and "Tazziberry", respectively, though I still prefer the original or "Chilean Guava" over both of those and the book's favorite, "murtilla"). I haven't seen it in the U.S., but apparently there is a growing demand in Japan. The cherimoya, it seems, is finding is finding its way to American markets, and the cape gooseberry (Physalis peruviana) is becoming a valuable crop in East Africa and Southeast Asia.
The other means by which these little-known species could have an impact is as breeding material for crossing with the established temperate crops. Several promising Rubus species could be crossed with blackberries and raspberries (the results of such work so far have been disappointing), and the capuli cherry (Prunus capuli) might have potential in the breeding of the various stone fruits, though that research has scarcely been attempted to date. The highland papaya and the various native blueberries might also contribute useful features to their respective relatives.
I'm probably a little more fixated on fruit than some people (okay, almost all people), but it makes me bizarrely happy to think about all the hundreds of fruit species out there that I have yet to try, and that science has yet to try to understand. There's so much variety out there, and we've only just seen the tip of the iceberg (this doesn't just apply to fruit, of course). And I think that's pretty cool.
(And no, that wasn't intended as a bad play on 'iceberg'. I just think it's cool.)