Think everyone just does that with satellites anymore (correct me if I'm wrong), though as previously mentioned lower altitude equipment can probably kick up the resolution.
The U-2 spyplane is still in use today, and for the past several years, there have been rumors that the US is flying a successor to the SR-71, nicknamed the 'Aurora'. The planes are supposed to have higher imaging resolution equipment than the satellites, and can be easily tasked at short notice to go anywhere, as opposed to waiting for the target of interest to come into view of a satellite.
I have read many books on this over the years, and one of the saddest part of US spy overflights is the number of lost planes and crew over the decades. The number is considerable. There are credible rumors of planes being shot down over the Soviet Union and PRC and the crews eventually dying in Communist prison camps.