n98-magerun – the Swiss Army Knife for Magento
Command line tool. Updates admin passwords and creates admin users, shows conflicting class overrides, and dozens of other useful functions. Indispensable for Magento development.
Admin Login Log
Creates a sortable, filterable log of all the logins to the Magento admin area.
Add a url parameter, get a dump of the global config object.
Magento server discovery shell script. Useful for when you just logged into a server you know nothing about.
Uptime Robot – Free website monitoring
I’m not an affiliate or anything, I just really appreciate this site. I think it allows you to set up 50 alerts for free.