In the next few years, X-ray free electron laser (FEL) facilities are expected to proliferate all
around the world. These 4th generation light sources, based on linear accelerator technology, can provide coherent X-ray beams, femtosecond pulses and a brilliance ten orders of magnitude larger than storage ring based sources. New detectors will be needed to to take advantage of their features and let them fully deploy their probing power. This paper shall review the state of the art in the field of 2D X-ray imaging instrumentation, focusing on a selection of the large set of detector technologies and architectural solutions proposed for experiments at FELs. This will
include some recent outcomes from the PixFEL project, an R&D INFN-funded program aiming at the development of advanced X-ray imagers for applications at FEL sources.