I'm a fan of the concept of a space elevator. I'd love to be able to see this technology envisioned by Arthur Clarke in the 70's become reality some time before I die. One of the biggest obstacles to the creation of the a space elevator is a breakthrough in the material science necessary to build a tether.
There are some promising bits of work being done on carbon fiber and buckytubes, but the last I heard, there were scaling problems. Sure, we can generate a fiber a few millimeters long that's strong enough, but getting from there to 100,000km is still a really big leap.
What if someone genetically engineered a bacteria that had some chlorophyll in it and had a predilection for growing a buckytube tail? Now you stick a vat in the sunlight and start pulling the thread... Voila! space elevator tether!