TreeSizeTreeSize is pretty sweet.
Its advantage over the others is that on NTFS drives, it works on the MFT (Master File Table) and reaches extremely high scan speeds.
They have 3three versions of the product: FreeFree, PersonnalPersonal and ProfesionnalProfessional.
The free version don'tdoesn't have fancy visualisationsvisualizations and reports but should be enoughsufficient in most cases.