For German speakers here...

I would say the Michelin Red Guide for restaurants. Although it's most well-known for the high-end restaurants, they also have plenty of non-starred cheaper recommendations. Most of the guidebooks I see sold in stores here are simply German-language editions of various internationally published travel series. For general interest travel, I haven't found anything unique enough for a German-as-third-language speaker (like myself) to purchase. However, there are some cool guides for more niche interests. I hike quite often with my dog, and for this activity, I have found the Rother Wanderführer series invaluable. There's also a guidebook series aimed at bicyclists, but off the top of my head, I can't think of the name. EDIT: Wait, perhaps I misunderstood the question. Are you specifically looking for German-language guidebooks of Germany, or a guidebook in any language that thoroughly covers the country?

This may not be what you have in mind, but I have used the "Daytrips" series. They do include some restaurant recommendations.

I'd order the Baedeker city or regional guides from amazon. A friend brought me the new all-Germany one but I don't like it as much as my 12-year old one because this one is a big fat tome, really unwieldy. If you go to the German amazon you should find them all listed.

I bought the Marco Polo guide for Hamburg and was very impressed. However, I don't use restaurant recommendations and can't comment on its use for that.

The only guides I know of that cater to budget choices are lonely planet and rough guide (both English). I'm not a big fan of any restaurant recommendations in guides because they're dated before they're even printed.

I don't put much stock in guide books which might recommend a restaurant far away, when there are perfectly acceptable ones close by. I usually just browse the neighborhood, reading the menus that are posted outside. Occasionally, my host will recommend a nice place nearby. But whether you go to a specific recommended restaurant you find in a guide book, or whether you just browse the neighborhood restaurants, you need to know how to read the menus. The best guide I ever found for that is Marling Menu Master. Apparently Amazon and Barnes & Noble think it is out of print, because they want an astronomical price for it. I paid $10 for mine years ago, and I still see some websites offering it for that price.

Thanks everyone, I'll have a look for the Marco Polo guides.

Lee, thanks for the menu translation resource. I just ordered. It always astonishes me when things turn up on Amazon or eBay for hundreds of dollars when available from a known source for much, much less.

Thanks, Lee for that reference. The German one is exorbitant at Amazon.uk too, so I just ordered it at Waterstones in the UK for under £5. I haven't seen this line but your recommendation was so good I went ahead and got an Italian one and a French one from Amazon, too - each under £5.

For reliable restaurant recommendations in German also download the Qype app or check with qype.com.