When looking for a great or simply good restaurant, it is important to compare various guides. I have subscription to online Zagat guide. The subscription is very cheap and you have access to all the most important cities in Europe and USA. This guide is extremely practical for those who travel a lot. As I mentioned before, no guide can be perfect, but Zagat can be very useful when you know nothing in a city.
I also have the Michelin guide for France. This year i bought it for New York as well. Usually, the Michelin stars is a good and fair reference.
Speaking about French guides, i often read the Gault Millau guide. Despite the fact, that i don’t agree with some of their ratings( Like 20/20 for Marc Veyrat), I like the way they describe restaurants.
Some good online guides I would like to mention are www.gayot.com/; forums.egullet.com/ ( a great forum), http://www.economist.com/cities/ ( the Economist cities’ guide have very useful tips for business travellers).
