Note: I'm not sure if I have a core point, but I did find this thought provoking and wanted to post what I had worked out so far.
Based on the Wikipedia page about Iodine http://en.wikipedia.org/wiki/Iodine_deficiency , it sounds like figuring out a way to distribute Iodine to everyone better so that noone experiences an Iodine deficiency in childhood would be an example of a non eugenics method to raise IQ. Although I suppose that implies the problem is not "The technology to solve this problem doesn't exist." but "The technology to solve this problem isn't getting to everyone who would benefit from it." And that can be the case with other transformative technologies that Stuart_Armstrong mentioned. Some areas don't have access to vaccines, some areas do have access to vaccines but are opposed to them, some people do not let women in their area use some contraceptive methods...etc.
I guess a way to describe the problem is that "How do we get everyone in the world access to the technological developments that we have already generated?" has several cases which are not a low hanging fruit. Even If I came up with a new nanopill that provided intellectual benefits similar to resolving an childhood Iodine deficiency, that could be stacked on top of it for even more gains, I'd still have to find a way of getting that nanopill to everyone, but that would be the same kind of problem I would face getting Iodine tablets, Iodine rich food, or even Iodized salt to everyone.
Cross-posted at Practical Ethics.
This is an addendum to a previous post, which argued that we may be underestimating the impact of innovation because we have so much of it. I noted that we underestimated the innovative aspect of the CD because many other technologies partially overlapped with it, such as television, radio, cinema, ipod, walkman, landline phone, mobile phone, laptop, VCR and Tivo's. Without these overlapping technologies, we could see the CD's true potential and estimate it higher as an innovation. Many different technologies could substitute for each other.
But this argument brings out a salient point: if so many innovations overlap or potentially overlap, then there must be many more innovations that purposes for innovations. Tyler Cowen made the interesting point that the internet isn't as innovative as the flushing toilet (or indeed the television). He certainly has a point here: imagine society without toilets or youtube, which would be most tolerable (or most survivable)?
But the flush toilet can only be invented once. We might have access to talking super toilets with multi-coloured fountains - but all the bells and whistles are less useful that the original flushing toilet aspect. That's because flush toilets responded effectively to a real human need: how to dispose of human waste in urban areas. Once that problem is solved, further innovation is mainly wasted.
This suggests that while we may indeed be plucking the innovation low-hanging fruits, it might not be because we lack a supply of innovation, but because we're exhausting the easy demand for innovation. What current needs do we have that we're waiting for innovation to solve? What's problems are we facing that are as important as removing human waste from urban areas?
There seem to be very few. Maybe solving death and disease: and we can make a very strong case that medical innovation is indeed slowing. Poverty is another one; but it's not like we know of a specific technological innovation that would solve poverty, if only someone would develop it. We might want easy access to space, or effective alternative energies: but the way people and governments spend their money confirms that this is not a top priority for many. Even if we had teleporters, would future Tyler Cowens be writing that they're not as innovative as the car - and would they be correct, in that a teleporter is just a more efficient way of solving a problem that cars and airplanes had already partially solved?
In summary, outside of the medical field, I don't see any conceivable realistic technological innovation that would be as transformative as the flush toilet, vaccinations, birth control, telephones, cars and airplanes. We might have exhausted the low-hanging fruits in our desires.
EDIT: some have suggested "high-throughput atomically precise manufacturing" as a general solution to material poverty, which would be an interesting counterexample.