By changes do you mean DDL changes rather than data? We handle those using PowerDesigner - its a bit cumbersome, but pretty good at merging differences between schemas. Generated (database specific) scripts to produce the physical model are tagged in SVN as they are promoted from dev to test to release.
Paul, thanks for the response. Yes, I do mean DDL changes.
I am familiar with PowerDesigner. I have used ERwin in the past which also does a decent job. But both of those products are VERY pricey. Anything less expensive?