DARPA has recently published a complete descriptive summary of all of its (unclassified) programs, and some of it reads like a science fiction author's wishlist. It's a fascinating collection of programs and it makes for absorbing reading.
I've read a good portion of the report and while I find it impossible to provide a summary (it is, after all, a summary in itself), though I was particularly enthralled by how DARPA is attempting to exploit the intersection of biology, information technology, and physical sciences. For instance:
The Brain Machine Interface Program will create new technologies for augmenting human performance through the ability to noninvasively access codes in the brain in real time and integrate them into peripheral device or system operations.Essentially this means that they are attempting to create an interface in which a brain accepts and controls a mechanical device as a natural part of it's body. The applications for this are near limitless and, though designed for military applications (of the type you're likely to see in science fiction novels), this technology would be extremely valuable for giving paralysis or amputation patients the ability to control a motorized wheelchair or a prosthetic limb as an extension of their body.
As you might expect, many of the projects work along similar lines and could theoretically provide supporting characteristics to one another. For instance, it seems to me that a brain machine interface would be particularly useful if paired with the Exoskeletons for Human Performance Augmentation program, again creating something right out of science fiction. It also raises some rather interesting questions about our place in evolution, and whether making the transition to a cyborg-like species is inevitiable. I remember Arthur C. Clarke forwarding the idea that as technology progressed far beyond our capabilities, human beings would find a way to transfer their consciousness to a mechanical (or, given the amount of biological engineering going on, let's just say constructed) being, as these machines would be more efficient than the human body. Of course, that is quite far off, but it is interesting to ponder (and Clarke even went further, postulating that we would only spend a short time in our "robot" form and even transcend our physical form...)
Again, I found the biological technologies (as well as many of the nanotechnologies) that are being explored to be the most interesting buch. One such program is attempting to actively collect information from insect populations to map areas for biohazards, another is set to develop biomolecular motors (nanomachines that convert chemical energy into mechanical work at a very high rate of efficiency). There are a lot of programs that utilize BioMagnetics and nanotechnology to attain a better monitoring capability for the human body.
Some of these projects or ideas have been around for a while and many of them are still in preliminary phases, but it is still interesting to see the breadth of ideas DARPA is exploring...
Note: Some of the information in the report is out of date, notably with respect to the "Total Information Awareness" project which was later renamed "Terrorism Information Awareness" and is now defunct.