Taunus

Gimbacher Hof - Kelkheim - Traditional German food, set on a farm with horses, a garden, and a wide variety of cakes.  Several trailheads behind the restaurant lead directly up into the Taunus forest. 

Eberhards Scheuer - Bad Soden - great garden restaurant, good prices, local food, a bit hard to find

Restaurant Thessaloniki - Bad Soden - good Greek food

Valentins Flammkuchenhaus - Königstein - great variety of Flammkuchen toppings and flavors

Villa Borgnis - Königstein - German/International food in a beautiful park setting at the foot of the Königstein castle

The Lodge - Kronberg - upscale restaurant with some of the area's best beef

The Schlosshotel - Kronberg - for 'high tea' and other elegant occasions

Heidekrug - Oberursel - authentic Korean food

Sabai Sabai - Oberursel - authentic Thai food

Anaya Indian Kitchen - Oberursel and Bad Homburg - authentic Indian food

Wiesbaden

Benner's Bistronomie - located in the stunning Wiesbaden Kurhaus, definitely a great choice for special occasions

Dale's Cakes - Tiny but wonderful with a varied menu and homemade American baked goods (best Carrot Cake ever). Perfect for breakfast or lunch. Don't miss the secret garden out back in warmer weather.

Der Andechser im Ratskeller - Bavarian food in a cozy restaurant located under the Town Hall on the Marktplatzwin

Erawan - authentic Thai food at a beautiful restaurant

Manoamano - Amazing cocktails and pizza in a great atmosphere, perfect for a date night without the kids

Noir Finest Sushi Cuisine - delicious Asian Fusion 

Saytoune - great Middle Eastern food

Goldgasse (also known as Italian Alley) has several Italian restaurants with year-round indoor/outdoor seating. All are good, La Cantinetta and Aurum are recommended.

Frankfurt

Mona's American-style breakfast - best American breakfast in Germany right in Frankfurt

Mangetsu - authentic Japanese in a casual venue

Apfelweinwirtschaft Dauth-Schneider - Apfelwein restaurant in Old Sachsenhausen with traditional Frankfurt specialties like pork knuckle, schnitzel, and handkäse mit musik (look it up)

Das Noodle Ding - Homemade Chinese noodles & soups with spicy sauces in a simple dining space

Bar Shuka - Female-run cafe with funky decor and Middle Eastern fusion on a wooden patio

Margarete - great place to meet a friend for brunch, wine, and modern European cuisine

Trattoria Rustica - authentic Italian with fresh ingredients