If you want the very best of French cuisine in the Pasadena area, there is only one answer: Ritz Carlton Huntington. :-) Coupled with a romantic garden, a handsome bar, and elegant lounging area (and sometimes, live music), the food is exquisite. The best way to taste Craig Strong's internationally influenced creations is to get the tasting menu, which runs about $100 each (no wine). Of course, you can always simply get starters or entrees. Desserts, however, cannot be missed. He tests, makes, and produces everything - including purees and ice creams - himself.
Bistro K on Fremont has a really creative chef who produces some outstanding dishes at very reasonable prices (dinner there will cost at least 50 percent less than at the Ritz). It's BYOB, with no corkage charges. Only downside is the service, which is really slow (or if you prefer, European). But if you are looking for a long, leisurely meal, it's lovely.