An investment bank is a financial institution that assists individuals, corporations, and governments in raising financial capital by underwriting or acting as the client's agent in the issuance of securities (or both)

As per your demand here I am providing you the list of the Independent investment banks
-Allen & Company
-BBY Ltd
-Blackstone Group
-Brown Brothers Harriman
-Brown, Shipley & Co.
-BTG Pactual
-Cain Brothers
-Cantor Fitzgerald
-Canaccord Financial Inc
-Capstone Partners
-Centerview Partners
-China International Capital Corporation
-CITIC Securities
-Close Brothers Group
-CLSA
-Cowen Group
-C.W. Downer & Co.
-Daewoo Securities
-Defoe Fournier & Cie.
-Duff & Phelps
-Europa Partners
-Evercore Partners
-FBR Capital Markets
-Financo
-Foros Group
-Gleacher & Co.
-Greenhill & Co.
-Guggenheim Partners
-Guosen Securities
-Houlihan Lokey
-Imperial Capital
-Investec
-Investment Technology Group
-Janney Montgomery Scott
-Keefe, Bruyette & Woods
-Ladenburg Thalmann
-Lincoln International
-M.M.Warburg & CO
-Marathon Capital
-Mediobanca
-Miller Buckfire & Co.
-Moelis & Company
-Morgan Keegan & Company
-N M Rothschild & Sons
-Needham and Company
-Newedge
-Oppenheimer & Co.
-Panmure Gordon
-Park Lane
-Perella Weinberg Partners
-Peter J. Solomon Company
-Piper Jaffray
-Pottinger (Australia)
-Raymond James
-Robert W. Baird & Company
-Sagent Advisors
-Sandler O'Neill + Partners
-Sanford Bernstein
-Stephens Inc.
-Stone Key Partners
-Thomas Weisel Partners
-Vermilion Partners
-Wedbush Securities
-William Blair & Company
-WR Hambrecht + Co