SRD75

Once the Memory Usage Monitor plugin is activated, activating or deactivating any other plugin will display the memory used by that plugin. e.g:
Memory usage for WP Memory: 0.02 MB
For accurate memory usage breakdown for each plugin, you must activate or deactivate them individually; you will not see memory usage when bulk activating plugins.

Memory Usage Monitor

Displays memory/RAM usage for each plugin as they are activated and deactivated.

Bastien Ho

NOUS Open Usefull &amp; Simple

Not tested on non linux hosted sites !
WordPress monitoring, displays for the super admin, the server ressources on the (network) dashboard
<ul>
<li>hostname and distro</li>
<li>size of the wp-content directory</li>
<li>available memory</li>
<li>space used on linux partitions</li>
<li>process running on the servers</li>
</ul>

Ressources

Monitoring the server resources with dashboard widgets

Memory Usage Monitor vs Ressources