I would bring up
Bonn, the former capital city of West Germany. This was essentially an accident if you will, because Konrad Adenauer, the first chancellor of West Germany, personally was in favour of it, instead of Frankfurt.
In OTL, even after the capital was moved back to Berlin in the mid-1990s, a lot of ministries remained in Bonn, and the city also remains important due to hosting many institutions of the UN.
So, Frankfurt might have ended up as capital city of West Germany in 1949 as well, which means that Bonn would been rather insignificant except maybe for being remembered that Ludwig von Beethoven was born there. The same would apply for about any TL in which WWII is averted, or with an earlier POD.
Additional reasons, Adenauer lived in the vicinity; and Bonn was situated on the left bank of the Rhine, thus one bridge further away from the Red Army (note that these decisions were taken in 1948/49 before MAD) - Frankfurt is just behind the Fulda gap and Kassel, the less prominent third contender had little chance because it was ridiculously close to what Adenauer called "de Soffjetzone".
However, without becoming capital of the FRG, Bonn would very probably still grow. It constitutes the Southernmost tip of the Rhein-Ruhr-metropolis and would still be an economical and suburban extension of Cologne. I estimate it would be at least at 200,000 in 2011 (325,000 in OTL). Its population reached 100,000 in 1934 already, and most comparable West German cities managed to double their size since then, last but not least by the annexation of neighbouring communities.
Note that Bonn's population keeps rising despite the loss of the government. Few German cities do so nowadays.
Well, while nobody outside of Europe would know Bonn, it would not be insignificant. However, it would lack the obscene amount of Autobahnen on its territory.
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Frankfurt as a FRG capital would be an interesting thing. I assume it might manage to break the million-inhabitant-mark, and be it by managing to incorporate more of its vicinity. E.g. everything up to the Taunus range would ideally have become part of it. A political - financial powerhouse of that size would stand a far better chance post-1989 to retain the position of capital in a united Germany. Bonn had ridiculously good chances to do so because it was the status quo and a general scepticism towards the "Reichshauptstadt" Berlin. Frankfurt would have the additional advantage of being rather central. While in the FRG, Thurinigia is not far from there. And also, the river Main is proverbially called the "Weisswurst-Äquator", meaning it is the line which separates North and South in Germany.
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A word on Berlin. As soon as Berlin becomes a larger centre than Potsdam, which it has always been, it is hard to replace it as the centre for this part of Germany. As poor as Brandenburg is concerning its natural ressources, it will probably have a central city of at least 300,000. That is still just 10% of OTL Berlin. Other places would benefit from such a shift: Magdeburg, Frankfurt/Oder, Stettin - but most of all Leipzig. Leipzig should under such circumstances become Germany's #3, #4 or #5 city with a population of at least close to a million, similar to OTL's Cologne.
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Cities which might not have been....most places in the Ruhr District have rather arbitrarily chosen names. Any other village next to Bochum, Gelsenkirchen, Marl, Oberhausen, Herne, Bottrop, maybe even Essen could have ended up with boundaries within this conurbation which makes it a rather large city. So instead of the aforementioned names, we would be familiar with Wattenscheid, Schalke, Hüls, Sterkrade, Wanne, Kirchhellen and Werden. I tend to take Duisburg, Recklinghausen and Dortmund for granted due to them having been cities of some importance for centuries. Actually, Essen and Bochum are rather on the safer side, too.