The Rue Mouffetard is what the Left Bank / Latin Quarter would be if it weren't overrun by tourists. It starts at the charming Place de la Contrescarpe and runs south a few blocks on the far side of the hill from the Bd. St. Michel nonsense. The street is home to a bunch of student dive bars, "ethnic" restaurants (Greek, Chinese, Indian, ...) and several fondue joints. Some of these places are hideous (like Chez Papa, whose salad was dressed largely by the lettuce washing water), but if you choose carefully you can have a good inexpensive meal in a fun neighbourhood.
It's been cold, so last night Ken and I went for fondue at Assiette aux Fromages. 15€ gets you more melted cheese than you can eat along with a nice bit of ham and salad. There's lots of other things on the menu, some even not cheese-themed, but it's clear you come here for fondue or raclette. And they do fondue well. We'll go back if we have time.
PS: the blog title comes from an awful marketing campaign by the American Dairy Association. The theme was that any food could be made into a delicious meal just by adding cheese. I can't think of a more succinct summary of the American approach to food.