High-resolution LiDAR and IFSAR. You can download some US elevation data for free from the USGS[1], other countries may have similar datasets available.
http://elevation.fsdf.org.au/ is starting to get data from LIDAR on a more local level, NSW/Sydney has some point cloud data up (presumably not just elevation but buildings/man made structures?) with more coming online every month until July 2018
[1]: https://viewer.nationalmap.gov/basic/?basemap=b1&category=ne...