Status2k is supposed to be pretty good, although I've never gotten it to run successfully on 2 different servers. But, that's just me...I've read several people have had success with this package and like it.
Monitoring server uptime from your computer can only be limited in reliability, since at any moment it can be eitehr your host or your ISP that is acting up. A third party monitoring service should be better (at least in theory), and most of them monitor from several parts of the globe.
If you're just looking for service monitoring / host availability then I would also suggest nagios. However http://cacti.net/ is also a great tool for monitoring server performance and general stats. It works over snmp and can be configured to poll just about anything if you make the right templates. My favorite feature of it is the ability to select a portion of the graph and have it enlarged, pretty handy when looking at small intervals.
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