Yep, variety is key, but we've traveled all around Europe with just Rick Steves and Fodor's and have found that to be enough. It's a perfect mix for us. We love Rick! (I can't say that I'd use his hotel recommendations, though, now that we can afford nicer hotels.)

Damien, all of the above seem to be helpful, especially a visit to your bookstore of choice to "thumb through" many of the previously mentioned guides. I would also add the various Green Michelin Tourist Guides, which are highly detailed, illustrative, and very specific to the area or areas you intend to visit. Good hunting and good travels.