If you look at OPS / RAC (oracle clustering), beware that aside from the costs and complication involved, is that the clustered machines need to be in close physical proxmity, since they share the same disk storage (something to ponder in case somene flies a plane into your colo facility). If you're going to spread things geograpically, OPS/RAC really won't help. You can do the standby database thing for that (if you can partition the databases into two machines - have each serve their database, and also be the standby for the other. If one goes down, activate the standby). I've heard of some folks that use Sun's clustering technologies rather than oracle's for doing database failover.
5 9's is pretty serious stuff. I'd definitely find an expert in the field and pay the five grand for a day of their time
