To spot gigs in Paris, go there :
http://www.concertandco.com/vconcert...&vi=1&x=16&y=9
At the bottom of the page, change dates.
I'm not sure I understand properly the cool band venues line, so there I'd go : la Maroquinerie is a great place for gigs (Liars november 27; in the past : Built to Spill, Guitar Wolf); Elysée Montmartre (BRMC on the 20th; in the past : Sonic Youth - my first time seeing them, the Cramps, and, before we were born, wrestle games)...
Museums (don't know much about art galleries) : l'Orangerie at the bottom of les Champs Elysées, when you're about to walk into the Tuileries gardens; it's not a big one, you won't leave exhausted with the impression that you've missed much. There's also the musée Maillol (exposed photographies of Marilyn Monroe's last session when she was quite drunk, that was impressive).
More if needed.