I love California Grill--I think it's the most special restaurant there, for me, because the food is wonderful and the fireworks viewing gives me that "back in WDW" feeling. The sushi is a little variable--I have had it where it was really excellent a few times, and a few times where the nori was a little tough--but the chocolate lava cake is always superb.
I also really like the Brown Derby, although it is probably a poor deal on the dining plan, as it's a little cheaper than the other restaurants. Nevertheless, I always enjoy the "Old Hollywood" atmosphere, and the sesame ahi I had last time I was there was excellent.
I've also been to Artist's Point, Yachtsman Steakhouse, Jiko, and Flying Fish. I liked all of them, although less than the previously listed two. I might not have a fair memory of Jiko, as I suddenly started coming down with a hideous cold right as I arrived there! Flying Fish was probably my least favorite--I think I had some sort of potato-crusted fish that was nice but not that memorable.
I also really liked Bistro de Paris, but I don't think that's included on the dining plan. It was very good but excessivly expensive ($6 for water! Always ask first!)
I hope to fill in my card with Narcoosees and Citrico's this next trip...