Girls get away 2 1/2 days in Paris

Croque Monsieur will be pretty well the same anywhere. My favourite macarons (macaroons are a very different English biscuit) are at Pierre Herme. I find the Laduree ones are a bit too dry by comparison.

I think you and your girlfriends will like Le Grand Colbert. Their food is probably not the greatest you can get in Paris, but it's good and the setting is glamorous. I also like the Bistrot Vivienne, in the passage Vivienne which is close by.
There are so many restaurants in St. Germain area, check TripAdvisor for suggestions, or just go into one that looks interesting. My favorite place in this area is Cafe Deux Magots -- but more for just sitting at an outdoor table with a glass of wine and people watching -- though I have eaten there as well. It's not really a place for dinner.
For fun experiences:
I highly recommend having the hot chocolate at Angelina's on the rue du Rivoli. It is popular, there may be a line --try to go at an off hour, and not on Saturday.
If you like shopping, check out Galleries Lafayette and Printemps department stores, which are next to each other. Both have rooftop cafes where you can sit outside, enjoy a great view of the city and sip wine or coffee. Or if staying in the St. Germain area you should definitely check out the Epicerie at le Bon Marche. Fantastic food items from everywhere the best of the best. It's across the street from their department store, also great.
Also like Laduree tea room in St. Germain 21 rue Bonaparte (there is a nice one on the Champs Elysee also), where you can have lunch or buy a fabulous array of macarons to go! There is a Pierre Herme store near St. Sulpice (and elsewhere) that also has great macarons (note they are not cheap!)
Another interesting thing to do is go to the rooftop observation deck of the Montparnasse Tower for fantastic view of the city.
You will find Croque Monsieur and crossiants everywhere -- in my experience all are good!
Just a few ideas.

Yes, macaroons are not macarons.
Macaroons http://www.foodnetwork.com/recipes/ina-garten/coconut-macaroons-recipe3.html
Macarons http://www.foodnetwork.com/recipes/macarons-recipe.html

My favorite macarons were from Pierre Marcolini (slightly less expensive than the others, just as good). Jean-Paul Hevin were also good, and of course, Philip's choice of Pierre Herme (though they didn't keep as well if you want to take some home). What about chocolate?

Thank you all for your suggestions and opinions. Our trip is fast approaching and we are very excited! Merci!

The hot chocolate at Angelina's is an absolute must. Do not miss a chance to have it. There is an Angelina's inside Le Printemps Department Store which also serves a wonderful French onion soup. Those two items alone make a meal!