Frankfurt has several large shopping malls that are easy to get to with public transportation. Hessen Center, Nordwest Zentrum, Skyline Plaza, and My Zeil. There is another one farther outside of town called Main Taunus Zentrum, but it is harder to get to.
* Skyline Plaza is our newest mall. It is located right next to the Messe and is easy to get to by taking the U-4 and getting off at the stop called Messe. You can also take trams # 16 & 17 from the main train station. This mall specializes in high end stores, unique little boutiques, and offers a great food court on both levels, including the a Chipotle.
* My Zeil has the most unique architecture in Frankfurt. Lots of people are always taking photos, both inside and out. Huge, foodie area called Foodtopia on the top floor offering a tasty variety of cuisines, a fitness center on the top floor, and a plethora of fashion stores. For electronic needs, make sure to visit Saturn, as they have decent prices and a huge store space. Kids love the Lego store located on the ground floor! Rewe on the lowest level, is a huge grocery store open until midnight 6 days a week. New movie theater recently opened on the top floor too.
* Hessen Center is your basic shopping mall with 3 floors. Take the U-7 from the Hauptwache direction Bergen-Enkheim, and it stops right in front of the mall. Most of the big department stores have branches here, Kaufhof, H&M, Karstadt, etc.
* Nordwest Zentrum is about the same as Hessen Center, but a bit more open and sunny due to the huge skylights. Take the U-1 from the Hauptwache, direction Ginnheim and the train stops at the mall at an underground stop.