I think as a general overall on-line guide Citysearch is the best. Not sure how it compares in other cities. I'm in SF. While I love Zagut's search, the restaurant info seems like a very bad tourist book.
Anyway there's a feature I never noticed before on citysearch which gives national winners in each catagory. The link below is the best restaurant catagory nationaly.
Unforunately national category lookup is a little cludgy (best breakfast, best Italian, etc). You need to select a city, see the list from that city and then click on National Winners. That sounds confusing even to me.
So, on the following link, scroll to say, NYC.
Click on it.
A list of best of categories will appear.
Select a cataegory, say best breakfast, and click on it. All the best breakfast spots will appear for NYC.
Scroll to the end.
Click on National Winners
Best Breakfast places around the country will appear.
Or, you could just ask JoeH.
(For those new to Chowhound, chowhound JoeH has spent a number of years eating out around the world. A little while back, on the General Board, He posted a Best of List).