High Availability Solutions for Databases?

An anonymous reader asks: "What would be the best high availability solution for databases? I don't have enough money to afford Oracle RAC or any architecture that require an expensive SAN. What about open source solutions? MySQL cluster seems to be more master/slave and you can lose data when the master dies. What about this Sequoia project that seems good for PostgreSQL and other databases? Has anyone tried it? What HA solution do you use for your database?"