HDDScan is a free test tool for hard disk drives, USB flash and RAID volumes. The utility can check your disk for bad blocks in various test modes (reading, verification, erasing), predicting disk degradation before you have to call data recovery service. Program can display SMART attributes, monitor disk temperature and change such HDD parameters as AAM, APM, etc. HDDScan can read S.M.A.R.T. from most of USB, FireWire & SCSI HDDs and supports all major USB boxes.
SpaceSniffer is a freeWare (donations are welcomed) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are situated on your devices.