http://www.pingbrigade.com/. Not exactly profitable yet, but brining in some revenue.
It would be great to add some more locations around the world.
If you add monitoring and alerts I would probably pay. Not that much as its already a corwded space, but I think a cheap alternative could get traction.
I wonder if its possible to have a business model of only charging when it alerts you to a site being down? E.g. we just alerted you to a site being down. Donate and we will do it again! Dont donate and I will delay my alerts by 1 hour next time!
It seems like you could ad maybe 3 Square Button ads in various places and still be unobtrusive about it..
Don't get me wrong I don't sell online advertising or anything but your site design would make it really easy to add more inventory and have them still not be distracting.
In the mean time I may add more ads but I would hate to detract from the experience for the small userbase.