Mysql by itself has built in "clustering" though there can be significant limitations in it depending on your requirements.
I agree. The built in cluster has too many limitations to be useful, but MySQL master-master replication gives a very good alternative to a true cluster. We use it to deploy geographically redundant systems and it has worked very well for us.
Neil
-- Neil Aggarwal, (281)846-8957, http://UnmeteredVPS.net/mysql MySQL pre-installed on a virtual private server for $25/mo Unmetered bandwidth = no overage charges, 7 day free trial