Near the Sorbonne is a lovely restaurant called Pre Verre. It's not only delicious, but well-priced too (even with the awful exchange rate). For 27.50 Euros one can consume:
1. Cold pepper soup with raspberries & chives
2. Chicken marinated in ginger and sauteed with avocados
3. Flourless chocolate cake with creme anglais and molasses ice cream
It's also close to Saint Michel, which is a major thoroughfare and a fun place to hang out. It is home to the fantastic Musee Cluny, my favorite Monoprix* location, and a used book and music store that's open late. If you plan ahead, try hitting a few of the shops in the area before dinner too (they close around 6 p.m.)
P.S. Monoprix is what I refer to as the French version of Target. Nuff said.