XMM-Newton and Chandra observations have been showing that our old vision of clusters as peacefully relaxed structures is in most cases quite wrong. Coupled with optical and radio observations, these X-ray data show evidence for violent mechanisms. Results concerning several very different clusters will be presented here. Among them: Abell 85 has most probably undergone two or three mergers. Abell 3376 is even more complicated, its brightest galaxy being totally outside the X-ray emission and the X-ray and radio maps possibly showing movements in opposite directions, while Abell 496 has a much more relaxed appearance, with no clear evidence for substructure. Finally I will briefly describe our discovery of ClG J1205+4429, the most distant fossil group presently known.