Anyone know of a good, free, webserver monitoring app that could sit on a toolbar or vista gadget?

Disregard found one on the gadget downloads. Works nice, gives avg load for 1, 5 & 15 minutes

Care to share?

Care to share?
LOL.. I was wondering the samething. I'm sure it's something others on this forum can also benefit from.

Does anyone recommend a particular off-site monitoring solution?

There are companies such as SiteUptime who offer free monitoring with 30 minute checks. However, given the low price of paid-for solutions, it is worthwhile paying around $4/month for 5 minute checks. Packages like this are available from a number of companies such as ServiceUptime and JustUptime.

Theo,
Have you used these before?

Sorry for the late response - yes, I have used SiteUptime before and am currently using JustUptime. Both do a reasonable job, but I prefer JustUptime's logging system and their graphs - they display information incredibly effectively.
For around $3.95-$6.95 for a paid plan with any of these providers, you really can't go wrong. I don't use a free solution as I prefer to have a fast notification when anything goes down. JustUptime also offers SMS notifications and includes some in their plans.
Tell me how everything goes.

check out http://www.hotscripts.com for this kind of script.

Please take a look on Zabbix.
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Please take a look on Zabbix.
+1, assuming you are looking to monitor and configure the monitoring of your own boxes, and have a place off-network to host it.
Otherwise, SiteUptime as a 3rd party solution is great as mentioned, good reviews here for them also.

Zenoss and Zabbix - I use both here. Slowly moving over toward Zenoss as our monitoring of choice, but it's a slow process :)

We love Panopta. They're monitoring ReadyWire from something like 18 sources.

Sorry for the late response - yes, I have used SiteUptime before and am currently using JustUptime. Both do a reasonable job, but I prefer JustUptime's logging system and their graphs - they display information incredibly effectively.
For around $3.95-$6.95 for a paid plan with any of these providers, you really can't go wrong. I don't use a free solution as I prefer to have a fast notification when anything goes down. JustUptime also offers SMS notifications and includes some in their plans.
Tell me how everything goes.
Not all of the free services delay notifications. Actually, this is the first time I have heard that. Must look at justuptime if you like the presentation that much :D

Alternativly you can useNagios or Nagios based monitoring systems.

I dont clearly remember the name, but i think cerberus people came op with some "sit on windows system tray" monitor.
I used it long ago... but lost track of it now.

Is there one that will have an OS X client to show when servers are down?

Consider also programming your own monitoring application.
It's not so difficult and worths its time.

You may want to try out the Monitor Script made by HTB. I am starting to like their scripts and most of the software is rebrandable or comes with the option to get the source code so you can improve it as you'd like. Here is the link: htbsoftware.com/monitor.php.

I will suggest to check also Monitis monitoring service, which provides both exernal and internal monitoring, prices starting from 5 USD / month

The message above as "plumsauce" seems to have been indexed wrong. Must be something to do with the problems of a few months ago. So, please do not get the wrong idea.