There have been many times that I've taken a look in one of my Zen Cart's /logs (or /cache for Zen Cart v1.5.0) directories and found some debug log files that I wasn't previously aware of. This plugin allows an admin user to view (and selectively delete) any files with names that match:

myDEBUG-*.log
AIM_Debug_*.log
SIM_Debug_*.log
FirstData_Debug_*.log
Linkpoint_Debug_*.log
Paypal*.log
paypal*.log
ipn_*.log
zcInstall*.log
notify*.log

The plugin searches only in these directories for the matching log-files:

/cache
/logs
/includes/modules/payment/paypal/logs

Once installed, the plugin can be accessed by a signed-in and authorized admin user by selecting Tools->Display Log Files.

Note: Due to the potentially sensitive nature of the information contained in some of the log files, I suggest that you run your admin in SSL mode if you use this plugin.

Due the the number of files that can accumulate, only the most recent 20 are displayed by default. If you want to display more files at a time, edit the file /YOUR_ADMIN/display_logs.php and change line 23:

define('MAX_LOG_FILES_TO_VIEW', 20);

The tool allows the logged-in (and authorized) admin user to:

Sort the log files, either ascendingly or descendingly, by last-modified/creation date.
Select (via checkbox) and then delete only the log files selected.
Delete all log files currently being viewed.
View the contents of an individual log file.

It's been tested on Zen Cart v1.5.0 and v1.5.1 and will be submitted to the Plugins area for review today.