Gnome Partition Editor

GParted is the Gnome Partition Editor.

GParted is an industrial-strength package for creating, destroying, resizing, moving, checking and copying partitions, and the filesystems on them. This is useful for creating space for new operating systems, reorganizing disk usage, copying data residing on hard disks and mirroring one partition with another (disk imaging).

More information is available here, and screenshots are here.