There are a ton of options, so I'll mention a few from cheapest to most expensive.
You can set this up to ping from one host to another. You can view the statistics and it will show how many pings have succeeded and how many have failed. This run in IOS.
Open source management program-
NAGIOS I believe can do it.
Solarwinds Network Performance Manager-
This is one is my favorite. It will graph latency times and loss. It will ever calculate device/site availability so you don't have to. Nice webUI as well.
Hope this helps.