Canal st. Martin & La Villete, Jardin de Luxembourg in the morning, Barbes, Montmartre away from Sacre Coeur, Parc aux buttes chaumont, botanical gardens (near Gare de Lyon I think - it's been a while), Versailles gardens in early morning (immediately after they open the place - Trianon, Petit Trianon etc.), just about every other park but I don't remember the names anymore ,
la Defence, Institute du Monde Arabe, Centre Pompidou, Champ de Mars, Pere Lachaise.... I remember somene telling me about abandoned viaduct near Bastille, supposed to be nice
BTW Try not to piss off people that might hurt you
I did, three times in fact (not always my fault though) but it always turned out ok for me. It can become pretty scary.
Keep your cameras in a backpack if you ever feel unsafe or seriously our of place. Being chased by junkies, weird shop owners or a group of nervous teenagers is interesting
Keep a low profile on the metro as well, especially at night.
too many things, not enough time