From freelancer to team of two : best way to share/sync db?
Do not consider your database a development asset. Instead consider the code an asset. Make all changes to the database through code, have the code checked in into source control. Conflicting changes resolve as source merges. Rails migrations capture this philosophy pretty well. But it can be applied to any platform and any language, eg. Version control and your database.

This approach will solve not only your team work issues, but also deployment, QA, upgrade of live site(s), tracking history of database changes, explain the current database schema and so many more.