I checked around a bit (not too hard), but couldn’t find a Wordpress plugin to let you easily display / monitor the loads on your server. A high load means your website could be slow to load for users, causing them to click away from your site. I’m currently using it on this site to just check on how loads are doing from time to time.

You can display the load stats in combination with Wordpress’ inbuilt page execution time and query number:

Execution: <?php timer_stop(1); ?>s |
Load: <?php echo server_load(); ?> |
Queries: <?php echo $wpdb->num_queries; ?> calls

The plugin function used is generic, and so can be put into any php script:

Server Load Check (v1.0)