Found a list on TransferMarket of players available on free transfers this summer. Some interesting names. Several have been snapped up already. I don't know if the list is exhaustive, probably not but it's interesting anyhow.
Sami Khedira (Real Madrid -> Juventus)
Dani Alves (Barcelona -> resigned)
James Milner (Manchester City -> Liverpool)
Evgen Konoplyanka (Dnipro)
Maxi Pereira (Benfica)
Carlos Zambrano (Eintracht Frankfurt)
Alberto Aquiliani (Fiorentina)
Glen Johnson (Liverpool)
Ron Vlaar (Aston Villa)
Giampaolo Pazzini (Milan)
Sergio Romero (Sampdoria)
Marcell Jansen (Hamburg)
Yoann Gourcuff (Lyon) Remember when he was gonna be awesome?
Juan Vargas (Fiorentina)
John Guidetti (Manchester City)
Cristian Ledesma (Lazio)
Ilsinho (Shakhtar Donetsk)
Andrew Ayew (Marseilla -> Swansea)
Tranquilo Barnetta (Schalke)
Urby Emanuelson (Atalanta)
Sergio Sanchez (Malaga)
Danny Ings (Burnley -> Liverpool)
Teofilo Gutierrez (River Plate)
Philippe Mexes (Milan)
Hugo Almeida (Kuban Krasnodar)
Pierre Webo (Fenerbahce)
Mehdi Lacen (Getafe)
Sergio Garcia (Espanyol -> Al-Rayyan)
Hugo Rodallega (Fulham)
Manucho (Rayo Vallecano)
Pape Diop (Levante)
Zakaria Bakkali (PSV)
Lassana Diarra
Jonathan Biabiany
Antonio Cassano
Benoit Assou-Ekotto (Tottenham -> Saint Etienne)
Diego Colotto (Espanyol)
Jonathan Walters (Stoke City)
Iker Muniain (Athletic Bilbao -> resigned)
Jose Antonio Reyes (Sevilla -> resigned)
Andre Santos
Egemen Korkmaz (Fenerbahce)
Neto (Fiorentina)
Piotr Trochowski (Hamburg)
Joey Barton (QPR)
Nigel De Jong (Milan -> resigned)
Jan-Arie van der Heijden (Vitesse)
Seydou Keita (Roma)
Jonathan (Inter)
Lisandro Lopez (Internacional)
Javier Saviola (Hellas Verona -> River Plate)
Mikel Arteta (Arsenal -> did he resign?)
Joao Pereira (Valencia)
Alberto Bueno (Rayo Vallecano -> FC Porto)
Andoni Iraola (Athletic Bilbao -> MLS)
Isaac Cuenca (Deportivo)
Stephane Mbia (Sevilla -> Trabzonspor)
Aritz Aduriz (Athletic Bilbao -> resigned)
Sammy Ameobi (Newcastle)
Tomas Necid (Zwolle)
Jimmy Briand (Hannover)
Juan GOmez (Hella Verona)
Esteban Cambiasso (Leicester City)
Juan Albin (Veracruz)
Erwin Mulder (Feyenoord)
Sami Khedira (Real Madrid -> Juventus)
Dani Alves (Barcelona -> resigned)
James Milner (Manchester City -> Liverpool)
Evgen Konoplyanka (Dnipro)
Maxi Pereira (Benfica)
Carlos Zambrano (Eintracht Frankfurt)
Alberto Aquiliani (Fiorentina)
Glen Johnson (Liverpool)
Ron Vlaar (Aston Villa)
Giampaolo Pazzini (Milan)
Sergio Romero (Sampdoria)
Marcell Jansen (Hamburg)
Yoann Gourcuff (Lyon) Remember when he was gonna be awesome?
Juan Vargas (Fiorentina)
John Guidetti (Manchester City)
Cristian Ledesma (Lazio)
Ilsinho (Shakhtar Donetsk)
Andrew Ayew (Marseilla -> Swansea)
Tranquilo Barnetta (Schalke)
Urby Emanuelson (Atalanta)
Sergio Sanchez (Malaga)
Danny Ings (Burnley -> Liverpool)
Teofilo Gutierrez (River Plate)
Philippe Mexes (Milan)
Hugo Almeida (Kuban Krasnodar)
Pierre Webo (Fenerbahce)
Mehdi Lacen (Getafe)
Sergio Garcia (Espanyol -> Al-Rayyan)
Hugo Rodallega (Fulham)
Manucho (Rayo Vallecano)
Pape Diop (Levante)
Zakaria Bakkali (PSV)
Lassana Diarra
Jonathan Biabiany
Antonio Cassano
Benoit Assou-Ekotto (Tottenham -> Saint Etienne)
Diego Colotto (Espanyol)
Jonathan Walters (Stoke City)
Iker Muniain (Athletic Bilbao -> resigned)
Jose Antonio Reyes (Sevilla -> resigned)
Andre Santos
Egemen Korkmaz (Fenerbahce)
Neto (Fiorentina)
Piotr Trochowski (Hamburg)
Joey Barton (QPR)
Nigel De Jong (Milan -> resigned)
Jan-Arie van der Heijden (Vitesse)
Seydou Keita (Roma)
Jonathan (Inter)
Lisandro Lopez (Internacional)
Javier Saviola (Hellas Verona -> River Plate)
Mikel Arteta (Arsenal -> did he resign?)
Joao Pereira (Valencia)
Alberto Bueno (Rayo Vallecano -> FC Porto)
Andoni Iraola (Athletic Bilbao -> MLS)
Isaac Cuenca (Deportivo)
Stephane Mbia (Sevilla -> Trabzonspor)
Aritz Aduriz (Athletic Bilbao -> resigned)
Sammy Ameobi (Newcastle)
Tomas Necid (Zwolle)
Jimmy Briand (Hannover)
Juan GOmez (Hella Verona)
Esteban Cambiasso (Leicester City)
Juan Albin (Veracruz)
Erwin Mulder (Feyenoord)