You generally want to begin any legal research project by consulting secondary sources. This page provides links to some of the leading secondary sources in the tax field, including major treatises as well as practitioner-oriented resources.
BNA Tax Management Portfolios
Bloomberg BNA's Tax Management Portfolios are highly regarded resources that provide guidance on handling specific tax situations.
California-Specific Tax Treatises
General State and Local Tax Treatises
General State and Local Tax Resources