I was in a similar situation about 6 months ago. I didn't find anything off of the shelf so I contacted a couple of monitoring services. There's pretty many services but only a few that meet my requirements. I ended up going with Alertbot.com. They don't say that have a reseller program but if you ask, they do. I don't know if they accept anyone or if you must meet certain requirements. I choose them because they actually pick up the phone when you call, they are located in the US, the prices are resonable, and the interface is pretty easy to use. They also have so pretty big name clients so when I refer clients to them (I went with the co-branded option) it makes my company look good.