MHDD is the most popular freeware program for low-level HDD diagnostics.
MHDD supports these interfaces: IDE, Serial ATA, SCSI. Also there is a possibility to access an USB storage, there are drivers for emulation (USB->SCSI).
This software can make precise diagnostic of the mechanical part of a drive, view SMART attributes, perform Low-level format, bad sector repair, different tests and tens of other functions.
MHDD 4.5 (older version, but includes ATA/SCSI Terminal):