Seafood -- Anchor Oyster Bar & Seafood, 579 Castro St...a small, storefront of a place has some of the best seafood in the city. Completely neighborhood/casual.
Ah yes, GJ, completely agree, I second this place in the Castro, silly me to forget, jeez, live ten minutes away over the hill. And also in the Castro I'd try the
Woodhouse Fish Company on Market Street. Both are great places. Some folks swear by Catch, also in the Castro, more of a restaurant-style place, rather than oyster bar deal. Never been there myself, but it's worth the mention.
OK, last one ... considering most places in SF don't qualify as fine dining (ie, you'll get in in shorts, shirt and a nice credit card), if you want more of a restaurant, and a view to boot, you could try
Waterbar. Bit too pricey for my liking, but the location/view is just stunning, and with a credit card charging in pounds, it might not feel too outrageous. They have some really interesting dishes on offer. Armani suit definitely not required, from what I can tell.