I would like to run some kind of service monitoring for my server and few other servers/services. Basically I want to monitor availability and send mail, when avail. is bad. Is there any simple alternative to nagios in Ubuntu repo?
You can use ICINGA, It has all the option you have asked for.
Check the installation How to install icinga on Ubuntu 12.04 & Monitor remote host?
Just keep in mind install MySQL before installing it. Some time it conflict when installing.