I really love the Sacre Coeur, I took each of my visitors to this great spot. Most of Paris's sight seeing aim is to get you to the top of things. You can go to the top of the Arc de Triomph, Pompideau, Notre Dame and of course, Eiffel Tower.
All of them are great views but the Sacre Coeur is where my heart likes to go. It is a beautiful white cathedral perched at the end of Montemartre. I've done this trip from different angles seeing Montemartre first and then sitting on the hill, one of the few places you can step on the grass. You can enjoy the view and depending on the season and day watch all the tourists stagger up the stairs. There's three places around here that I would recommend depending on the time of day.
View Paris-visiting Sacre Coeur in a larger map
If you're hungry I recommend the most awesome Salad place. Marmite is easier to recognize but if it looks busy Le Relais Gascon menu is fantastic. They have salads like no other, giant size bowls that are a feat to finish usually all come with roasted garlic potatoes on top.
If you're hankering for a drink I recommend Marlusse et Lapin. A cute and funky independent bar where pints are only 3€. I would only venture here with someone else. It's the red light district of Paris and its up a little dark alleyway. You're sure to see some characters around. It's a very small place so the biggest group I've taken there is four people but if it's not busy you can fit six comfortably in the back all at the same table.
If a nice cafe during the day is what you want I recommend Fuxia. You can have three deserts and an espresso for 6€ here. You'll also pass by a nice little place with a beautiful piece of stained glass. If you're looking for any instruments this is also the district to be.
Also in the area is a concert hall, the Amelie cafe and a walk to moulin rouge.
If you click on the map all the places I've mentioned have been taged