Using QuietMan7's suggested list of additional tools, I've tested the following, with results listed accordingly. The system used for testing was a Windows 7 Pro (32-bit) box with a Seagate external 2T USB drive.
I want to emphasize that I'm not judging the effectiveness of any of these tools; my sole reason for testing was to find which scanners could scan user-specified drives (rather than simply scan everything).
Granted, simply scanning everything is probably the safest thing to do, but in most cases in my work it's unnecessary. As mentioned, I usually run these tools from a known good system, pointing the tools to an external USB caddy that holds the infected drive.
The results are below, listed in no particular order. The green ones are the ones I may start using regularly during AV operations. Again, it's not that the others are bad - I'm not passing a judgment on any other than the ones that I had issues with.
ESET Rogue Application Remover (command based) - does not allow drive selection
VIPRE Rescue Scanner (command based) - does not allow drive selection
SuperAntiSpyware - allows drive selection
Hitman Pro - does not allow drive selection
McAfee Stinger - allows drive selection (amazingly slow, however)
Kapersky Virus Removal Tool - allows drive selection
Microsoft Emergency Repair Tool (MSERT) - allows drive selection
Norman Malware Cleaner - allows drive selection. Crashed the first time I tried it. Redownloaded, tried again. Scan proceeded without problems--not sure what caused the first crash; the original download was a few days old, perhaps like MSERT they have a limited life. Requires email address to download.
Panda Cloud Cleaner - does not allow drive selection
Secure APlus = allows drive selection. Anti-virus seems to be a secondary function of this one.
Trend Micro Anti-Threat Toolkit (command based at first, then GUI) - does not allow drive selection
Tools with Issues--
Trend Micro System Cleaner (command based at first, then GUI) - allows drive selection. It told me "Install failed" but then seemed to continue on to a command window. The date file on the GUI says it's from January 19, 2010...if that's accurate and not just a bit of overlooked coding, that limits this tool's usefulness a lot.
Sophos Virus Removal Tool - "Error 1606 - Could not access network data." Redownloaded, tried again, same result.
Windows Defender Offline - this is more of a rescue tool, like Norton Power Eraser, designed to be run on an infected system rather than as a simple scanner. It does allow drive selection. This would be more useful in phase 2.*
MicroWorld ESCan AV - want an awful lot of information before allowing download. Downloaded anyway. Allows drive selection, but definitions are from April 2014. IOW, if you run this, it's not just download, choose drive and run, check the settings first. Normally when one downloads, say, MalwareBytes it goes out and updates its definitions when you run it. Not sure why this one doesn't. You can manually update. When I ran this, I watched to see if it updated itself prior to a run but it didn't.
Dr.Web Cureit - want way too much information from me just to download their product. Skipped.
Hitman Pro Kickstart - not tested. Seems a bit too specific for my purposes, but I'll keep it in mind for ransomware.
Well, I can definitely see adding some of these to the scanning routine. And hopefully someone else will find this information useful.
*Phase 2 - Once scanned externally, the drive is put back into the host system, and after either booting normally or in Safe Mode, more tools are run. These tools include AdwCleaner, JRT, ComboFix and whatever else might be needed for a thorough cleaning. I may add some of the tools listed above that don't allow drive selection.