Looking for a guide to best classical recordings

Nick, I own and use the following guides:
(1) Gramophone Classical Good CD Guide. British. Over 1300 pages. (There is also a shorter version of this book on opera only.)
(2) Penguin Guide to Compact Discs. British. Over 1500 pages.
(3) Classical Music on CD: The Rough Guide. British. About 500 pages. (There is also a shorter version of this book on opera only.)
(4) Jim Svejda, The Record Shelf Guide to Classical CDs. American. About 900 pages.
All of these are fat, large-format paperbacks and all are well worth having and using. Of course they often don't agree, but what is "the best" performance is obviously a subjective judgment. Books like these will certainly alert you to famous, celebrated performances that stand out from the pack. Good luck and good listening.

I have the Penguin Guide, the one that came out in '96, I was also just given The Rough Guide by my wife. The Rough Guide says it is good for people just getting started in classical and I agree.
I find the Penguin guide to be very good, giving alot of options or reviews of a particular piece most times. The problems I have with Penguin are the updated volumes usually contain very few new entries and soemtimes things that are reviewed are out of print or very hard to obtain in the U.S.A., but all in all in my view Pengiun is very good.
I think it is a good idea to focus on a particular style, era, or composer, then buy what you like. I think you will find that every once in a while, you read a review, it sounds good, you buy it, and then you listen and you don't like it. This happens to me every so often and to me its just part of the classical music thing.
If you can find a shop that sells used cds in your area that is a very good thing to do and you can usually listen to them in the store before you buy.

I find that Grammophone Magazine is really useful. I've purchased a fair number of their "editor's best" CD's and have been delighted. Their website also has some suggestions. Although I've never read it I imagine their guide to classical music CD's would be excellent.