If you’re not familiar with Munin, it’s a bit like Nagios, (and if you haven’t heard of Nagios, it’s a network monitoring tool). Munin is particularly nifty because it’s easily extensible in pretty much any language that takes your fancy; Perl seems to be the favorite, but Python is also used.
You can check out the plugins on Distilled’s Github account (parent company of Adverts.ie, Boards.ie, Daft.ie and TheJournal.ie).
There’s a bunch more there that Conor McDermottroe has written for MySQL, Snort, IMPI and FreeBSD too which you might also be interested in!
Edit (2012-11-06): Github user kura has written an installer for these plugins available here: https://github.com/kura/solr-munin