Take a look at PricewaterhouseCoopers Worldwide Tax Summaries.

Look at KPMG:

• Corporate Tax Rates Table: global corporate tax rates, 2006 to present
• Individual Income Tax Rates Table: global individual income tax rates, 2006 to present

Check out the OECD Tax Database.

Use World Development Indicators from the World Bank.

• Select Country.
• Select Series.
  • Search tax rate.
• Select Time.