Web based application redundancy

Today I have been looking into redundancy for a web application that is hosted at rackspace. Rackspace offers 2 load balancers: Webmux and Cisco 11501. The application runs on windows IIS and from there you need multiple machines that run as a web farm. The key to a web farm is to store the session data in the database. To handle redundancy at the database layer, a high end solution is to use a SAN and then have two (or more) database servers that use Sql Server clustering. Another lower cost solution is to use database mirroring with a third witness server that handles the fail over. Rackspace also has 2 levels of support: managed and intensive, which is more expensive. Intensive will support a SAN with SQL server clustering, but they don't support the database mirroring.