MMM (Multi-Master Replication Manager for MySQL) is a set of flexible scripts to perform monitoring/failover and management of MySQL master-master replication configurations (with only one node writable at any time).
The toolset also has the ability to read balance standard master/slave configurations with any number of slaves, so you can use it to move virtual IP addresses around a group of servers depending on whether they are behind in replication.
The current version of this software is stable, but the authors would appreciate any comments, suggestions, bug reports about this version to make it even better. Current version 2.0 development is led by Pascal Hofmann. If you require support, advice or assistance with deployment, please contact Percona or Open Query.