I have been experimenting with NAGIOS3 on Ubuntu (I will write a how-to-install on NAGIOS later) and it has served me very good in monitoring my 7 VPS from different providers in different part of the world. I have already recorded 3 hours of downtime from ThrustVPS which is a great deal for me. I now know which VPS has the best time and which ones have hiccups (e.g. my 2Host VPS gave me two unreachable notifications but the VPS was running and still reports the uptime as 4 days).
Since I use twitter more, even when Im on the road, notifications via email is a bit slow for me. Luckily I found a great tutorial online to do that.
I registered a new twitter account for this purpose @twitgios, made its tweets private and followed this newly created account from my primary twitter account @asimzeeshan. Configured NAGIOS with twitter-nagios plugin and Viola! it now tweets status and updates as mentions to my personal account.