Get a carry out, sit at the Eiffel Tower, jobs a good un
If your after something a little bit different, or rather one of your mates is :cough cough: then get the fired up to the Pigalle area. Every size, shape and colour up there

And my excuse for being there for two nights was my hotel was slap bang in the middle of it and only £15 a night
To be honest I didn't see a huge amount of Paris but did go for a gander on the Wed morning before the drinking started. Great city to walk about in, some impressive sites but no idea how much I would be wanting to stride about in, in this sort of weather.
If you are going to the Louvre, get there as soon as it opens. I was sitting outside it for a bit about 10am and it was getting busy.
Montmarte is a fair bit away from the centre I think, wasn't far from where we stayed. And we were about 8-10 stops from the central area. You get to see a big church on a hill (Sacre Couer) but thats about it I think. But you are near the RLD
Don't bother going to PSG's ground, its just a normal ground, nowt special, nothing of interest there. Stade De France is a bit out as well. If your coming in by train from CDG you pass it.
Avoid all gyspy/Romanian beggars who bend down in the street in front of you and then ask you if you have dropped the most hideous "gold" ring ever created. Also avoid gyspy types who come up to you with bits of paper asking to read something. While your doing so her accompliace will be dipping your pocket. There was loads round the ET when we were there, I was actually convinced one of the soldiers on duty was going to shoot one of them, he was getting well pissed off with telling them to fuck off every 30 mins. He had a big fuck of machine gun strapped across his chest and I could see him losing the rag and bludgeoning a few of them with it or just opening up on them.