In Brac - Taverna Riva, located along the water's edge, near the Hotel Kastil. Excellent food. If you can, order 'octopus under the bell' a day in advance - magnificent, the flesh was so firm and tender and succulent. The roasted vegetables and rich sauce, so good. The owner wine recommendation were right on. I also like Gust - located one street, across from the entrance to the Hotel Kastil. The lobster salad, the salted sardines, the mussels, the steak - all very good - the only thing I would steer clear of is their house wine. If you're tooling around the island - there is a wonderful restaurant on the other side of the island called Toni, http://toni-dol.netfirms.com/index.html, near Postire. One of the owner's brought out a octopus draped over his arm asking us if we would like to start with it for lunch (YES)
In Hvar Grad - the Golden Shell, Macondo and Menego, http://www.menego.hr/, are all good choices. You'll want to make reservations at Macondo - it 's very popular. There is a wonderful restaurant in Pitve called Knoba Dvor Dubokovic - the views looking out over vineyards towards Brac are mesmerizing. East of Jelsa in the abandoned village of Humac is Knoba Humac - incredible lamb, strong Plavic wine, fruity olive oil - a true Croatian experience.
Can't help with Trogir because I'm going this September.
As for fish - scorpino and orada are my faves.
In Zadar - I recommend Kornat, Liburnska obala 6 - updated Dalmatian dishes at reasonable prices. Located on the water's edge of the historic center, near the ferries.
I found this list to be very helpful regarding Zadar: