Scales and Shells is very good. Make sure you bring cash, as they don't take credit cards.

http://www.scalesandshells.com/

looks fantastic, thanks! Now I need one for the second night...

The Mooring:
www.mooringrestaurant.com

Clarke Cooke House: (Candy Store)
www.clarkecooke.com/clarke_cooke_house/clarke_candy_grill.aspx

Black Pearl: (Tavern)
http://www.blackpearlnewport.com/

Definitely, Castle Hill Inn for one nite - reserve a table "at the window".
Scales and Shells is great - very casual but there mesquite grilled fish is the best.Be advised that the menu is all fish and shellfish.
The Moorings - MMMmmmmm..get the "bag of donuts" appetizer. The scallops are excellent and so is the veal chop.
If you want a great steak - 22Bowen.

I also like the Cooke House and the Black Pearl.

The West Deck is also good for casual seafood but I'm not sure they're open this time of year.

Oh, and if you're looking to splurge, don't miss the Spiced Pear at the Chanler Hotel.

http://www.spicedpear.com/home.html

Interesting, I wouldn't describe the West deck as casual seafood unless you mean outside? I consider it one of the more upscale newport places-- white linen table clothes and excellent higher end food. Although they serve seafood, i wouldn't call it a seafood restaurant. Granted, a very loud bar sits right outside it, but i find the inside to be a nice contrast to that.

For good seafood with a view, i'd choose the Mooring- just b/c it's on the water. The Spiced Pear is great, but it is very very pricey and in my opinion quite formal for newport. castle hill itself is a wonderful option.

We had a beautiful evening at Sardella's... I can't rave enough about the food or the people. The lobster stuffed ravioli made me re-think my definition of Italian seafood! The restaurant is on Memorial Boulevard, which is a nice walk from water.

Just FYI, all these restaurants mentioned have great reps, but scanning the menu I see some fish that can't possibly be very fresh, as they are not local species. For example, the Castle Hill Inn lists red snapper as a menu choice. The closest red snapper to RI is about 1200 miles away; the "freshest" this fish could be would be three days old. So if "fresh" is important to you, ask the server for what is locally caught and in-season (thinking cod, flounder, tog). Also, since it is dead of winter, the harbor view you get by eating at the Moorings isn't anything like that you get during boating season, so I wouldn't eat there just because of the view (food is great, though).

I hate to be the lone dissenter but last year I took my mom to Scales and Shells for scallops and we were both significantly underwhelmed. Over-priced and nothing to brag about. Sorry.

The Mooring serves wonderful seafood. Scales and Shells doesn't accept reservations, and is very popular, so expect a long wait. What is great about Newport is that much of the seafood is fresh and local.