One of the best times for seeds to grow is after a forest fire. There's plenty of nutrient-rich ash and daylight.
The same principle applies to startups. Many times, you can find great opportunities in the wake of spectacular flameouts. Palm revolutionized handheld computing after the spectacular failure of Go. Zappos built a billion-dollar business after other dot bombs like eToys flames out.
What space do you think represents fertile ash today? Solar? Twitter clients?