What are some best monitoring tools available for mysql? I have a setup a linux mysql server and would like to monitor it. I found percona plugins for nagios and cacti. Are there any other tools available?
Have you looked into MySQL Enterprise Monitor? Or are you only looking for freeware?

EDIT: You could also use this comparison chart from Wikipedia to pick one based on your needs:

http://en.wikipedia.org/wiki/Comparison_of_network_monitoring_systems