Please send me top 20 finance research topics thar are very popular.

You don't want popular -- you want unique, so you stand out from the crowd.

Islamic finance and bank system, microfinance, Grameen Bank, corporate finance, SME financing, project financing, credit appraisal process of banks, financing in an emerging market (Russia, China, India, or Brazil), the growth of hedge funds, Internet banking, CSR of the banking industry, risk management, global accounting standards.