A lot of repair and recovery options are available from the advanced boot menu itself- sfc scan, startup repair, command line access etc. In case the system cant boot at all, the Windows 7 install dvd lets you run these options when you boot off the dvd- Carl has already linked the repair install tut.
If you dont have a Windows 7 disk or dont want to use one, download the Windows 7 repair disk (about 140 mb download) from the Neosmart site, thats a win PE that lets you use System Restore, Complete PC Backup, automated system repair, and a command-line prompt. Download Windows 7 System Recovery Discs — The NeoSmart Files
If you are looking for something in the way of diagnostics, you could try Ultimate Boot CD. Ultimate Boot CD - Overview
For data recovery in desperate situations use a live linux distro cd/dvd such as knoppix or Ubuntu.
When you said ERD commander, i immediately thought of MSdart (MS diagnostics and recovery toolset). Unfortunately, its not free, worse its bundled with the MSDOP which is available only to VL customers or technet/MSDN customers. How to recover a non-bootable Windows installation – The Microsoft Diagnostics and Recovery Toolset - 4sysops