Thought this may be of interest to you, an uptodate list of some of the top ATP and WTA players, and the rackets they use/types of strings and a rough idea of the tension.
I think the tensions may vary slightly depending on where they play, so this list was taken from this years Wimbledon and Montreal events- may be different at this years US Open.Look at the difference though for example between Marin Cilic at 61lbs and Marcos Baghdatis at 46/51 lbs. 60lbs is about 27.2kilos.
My rackets are strung at 24 kilos, which is about 53lbs- the same as Juan Carlos Ferrero..that will do me!

Latest Update: Wimbledon/Montreal Masters- August 2011
Mario Ancic Yonex RDS 002 Tour Luxilon Big Banger Original 62lbs
Marcos Baghdatis Tecnifibre T-Flash 315 Speedflex Tecnifibre X-One BiPhase 46/51lbs
Tomas Berdych Head YouTek IG Instinct Luxilon Big Banger Alu Power 55lbs
James Blake Donnay Prototype Luxilon Big Banger Alu Power 68lbs
Bob Bryan Prince EXO3 Rebel Prince Natural Gut/Luxilon Big Banger TiMo 56/52lbs
Mike Bryan Prince EXO3 Rebel Prince Natural Gut/Luxilon Big Banger TiMo 54/51lbs
Juan-Ignacio Chela Babolat Pure Storm Team Tecnifibre Spinfire Maxi Power 58lbs
Marin Cilic Head YouTek Radical MP Babolat VS Touch 61lbs
Kim Clijsters Babolat Pure Drive Team Babolat VS Touch 58lbs 
Nikolay Davydenko Dunlop Biomimetic 200 Plus Unspecified Black Polyester string 51lbs
Juan Martin del Potro Wilson [K] Six.One 95 Luxilon Big Banger Alu Power 62lbs
Novak Djokovic Head YouTek IG Speed Pro 18×20 Babolat VS Team Natural Gut/Luxilon Big Banger Alu Power Rough 55/52lbs
Roger Federer Wilson Six.One Tour BLX Wilson Natural Gut/Luxilon Big Banger Alu Power Rough 48.5/44lbs
David Ferrer Prince EXO3 Tour Luxilon Big Banger Original 51lbs
Juan Carlos Ferrero Prince EXO3 Tour Luxilon Big Banger Original 53/51lbs
Richard Gasquet Head Microgel Extreme Pro Luxilon Big Banger Alu Power 58lbs 
Robby Ginepri Babolat Pure Storm Team Babolat Pro Hurricane/Babolat VS Team 64lbs
Fernando Gonzalez Babolat Pure Storm Team Babolat Pro Hurricane 60lbs
Tommy Haas Head YouTek Prestige Pro Babolat VS Team 75lbs
Daniela Hantuchova Prince EXO3 Tour Babolat VS Touch 58lbs
John Isner Prince EXO3 Black Tecnifibre Pro RedCode 62lbs
Ana Ivanovic Yonex Ezone Luxilon Big Banger Alu Power 54lbs
Jelena Jankovic Prince O3 Speedport Pro White Luxilon Big Banger Alu Power/Prince Natural Gut 64lbs
Petra Kvitova Wilson BLX Tour Luxilon Big Banger Alu Power 57/53lbs
Svetlana Kuznetsova Head Extreme Pro Luxilon Big Banger Alu Power 57/55lbs
Sabine Lisicki Wilson BLX Blade Luxilon Big Banger Alu Power Rough/Wilson Natural Gut 52/50lbs
Ivan Ljubicic Head YouTek IG Extreme Pro Babolat Pro Hurricane 69lbs
Michael Llodra Wilson BLX Pro Tour Babolat VS Team 52lbs
Gaël Monfils Prince EXO3 Rebel Luxilon Big Banger Alu Power 57/55lbs
Andy Murray Head YouTek Radical Pro Luxilon Big Banger Alu Power Rough/Babolat VS Team 62lbs
Rafael Nadal Babolat AeroPro Drive GT Babolat RPM Blast 55lbs
David Nalbandian Yonex RDiS 100 Luxilon Big Banger Original 64lbs Jiri Novak Völkl Tour 10 Mid Plus Luxilon Big Banger Alu Power 64/62lbs
Nadia Petrova Babolat AeroStorm Luxilon Monotec Supersense 62lbs Mark Philippoussis Head i.Prestige Babolat VS Team 75lbs
Andy Roddick Babolat Pure Drive Roddick Babolat Pro Hurricane Tour/Babolat VS Team 73/61lbs
Maria Sharapova Head YouTek IG Instinct Babolat VS Team/Babolat RPM Blast 62lbs
Robin Soderling Head YouTek Radical MP Luxilon Big Banger Alu Power 56lbs
Radek Stepanek Bosworth Custom Pacific Prime Gut 55/53lbs Paulo Suarez Prince O3 Tour Prince Tournament Nylon 65lbs
Janko Tipsarevic Tecnifibre T-Fight 325 VO2 Max Tecnifibre BlackCode 57/55lbs
Jo-Wilfrid Tsonga Babolat AeroPro Drive GT Babolat VS Team 59.5lbs
Serena Williams Wilson Blade Team BLX Wilson Natural Gut 66lbs Venus Williams Wilson Blade Team BLX Wilson Natural Gut 66lbs
Caroline Wozniacki Yonex VCore 100S GT Babolat Revenge/Babolat VS Team Natural Gut 57lbs
Vera Zvonereva Prince EXO3 Black Gamma Zo Sweet 57/60lbs