Just off the top of my head...

Christophe (Mediterranean) - One of the "star" restaurants with one michelin star. The food was excellent and of great quality, with nice old atmosphere, but the service dry and impersonal (think French, but not quite as disasterous). Not hip, but rather expensive. Some dispute whether price matches the quality of the overall experience.

Cafe Roux (French) - Art Deco, informal-style restaurant with a great view of the canals (one a night with no wind the lights reflecting into the canals make for a fabulous view). Well regarded with very attentive/professional staff.

Utrechtsdwarstafel (French) - The owner/chef/whatever is known for matching excellent quality wines with good food and set menus. Not a hip environment, and more non-nonsense and pragmatic, simply elegant.

d'Vijff Vlieghen (Dutch) - Sort of a gaggle of old, small and typically Dutch houses turned together into a restaurant. Rather like how the Pulitzer is a maze of rooms built into several buildings. Very quaint and very Dutch. Also typically Dutch food, but then not quite so bland as usual.

A Fusion (Fusion, duh!) - A predominantly Chinese fusion restaurant. IMHO typical fusion: quality of food not high, but certainly not bad, and enough to satisfy one's tastes. Seemed quite trendy, and on the main square, and prices not too high either.

Blue Pepper (Indonesian) - IMHO one cannot miss Indosesian cuisine in Holland. This place serves it up right, in a not too kitsch setting, the right portions and nice quality. Definately not hip/trendy though. In fact, I doubt there are any hip/trendy Indonesian restaurants. Pricey though, and certainly there are cheaper alternatives.

Come to think of it, not many of these are so very hip or trendy, and I know of very few such places in Amsterdam. Maybe mainly because I personally have found the food in such places to generally be over-priced and served up by people who can barely boil water at home, lest cook restaurant quality meals. I think London does much better in that department. Hope this helps a little.

And if you really like mussels... come to my house and I will cook up a storm right in the dunes in the south of the country.