MySQL Performance Monitoring
If  you're looking for graphs, Cacti (or Munin) will work. I've personally only used Munin.

However, I wouldn't put much stock in graphs to troubleshoot problems that arise. If it's showing in the graphs, it's been going on too long.

I would get familiar with the maatkit or percona tools (I think percona is a fork of maatkit) for trouble shooting problems.