European Night of Museums on May 21st in which a hundred or more museums across the Ile-de-France region keep their doors open afterhours:
http://traduction.culturecommunication.gouv.fr/url/Result.aspx?to=en&url=http://nuitdesmusees.culturecommunication.gouv.fr

Fête de la Musique on June 21st- Enjoy free music on the longest day of the year! Expect big concerts in top Venues in Paris as well as amateur musicians on every street corner of Paris:
http://traduction.culturecommunication.gouv.fr/url/Result.aspx?to=en&url=http://fetedelamusique.culturecommunication.gouv.fr

We Love Green festival (rock to electronic) on the 28th and 29th May at the Parc de Bagatelle:
http://www.welovegreen.fr/en/

The Weather Festival on the 3rd, 4th and 5th June for techno lovers:
http://www.weatherfestival.fr/en

Solidays festival (ranges from rock and pop to electronic music) on the 24th and 26th June at the Longchamp racecourse:
http://www.solidays.org/

Jazz à Saint-Germain-des-Prés festival on the Left Bank from 19th to the 31st May
http://festivaljazzsaintgermainparis.com/home/

Peacock Society Festival in the Parc Floral de Paris from July 13th to 17th for electronic music fans:
http://peacocksociety.tumblr.com/

Bastille Day on 14th July includes a military parade in the morning on the Avenue des Champs-Élysées, a firemen’s ball in the evening, and between 11pm and 11:30pm the spectacular fireworks at the Eiffel Tower and Trocadéro
http://en.parisinfo.com/discovering-paris/major-events/bastille-day-in-paris

Rock en Seine festival held the 26th, 27th and 28th of August at the Chateau de Saint-Cloud park:
http://www.rockenseine.com/en/