So do I, constantly. Not that I've ever been there...

I don't know what your Italy trip includes, but Florence is a must, and a few days more for other places in Tuscany (Siena, arguably Pisa, some of the lovely villages like San Gimignano, Monteriggioni etc. ) would be good too.

As mentioned above, there's lots to be seen and done in France while still avoiding the snotty Parisians. I would also recommend Belgium and the Netherlands, but I might be biased. Still, Amsterdam would rank high on most tourists' lists, I'd think, and Belgium does have great food and art/history (and not just in Bruges, either). Amsterdam, Rotterdam, Maastricht, Antwerp (in which I'd be happy to show you around), Ghent, Brussels and Bruges are all definitely worth at least 1-2 days. Though it'll depend on your personal preferences which ones of those you like best.

In Germany, Berlin is very much a hot spot for tourists again - world class museums as well as a world class nightlife and supposedly (haven't been there in fifteen years) a really nice atmosphere. Munich's also supposed to be good, and there are plenty of lesser-known/smaller cities which are nice. Among the ones that I've seen, I'd recommend Freiburg im Breisgau, near the Swiss and French borders, and also near the big Black Forest, and also Aachen, near the Dutch and Belgian borders (known as the capital of the empire of Charlemagne way back in the 9th century AD).

I can't say much about most other countries, except to recommend Wroclaw in Poland if you're in that region, as well as Krakow (which unlike Wroclaw I haven't personally visited, but it's relatively nearby, and much better known). Lisbon in Portugal, but that might be a bit out of your way. Then of course Edinburgh and Glasgow in Scotland - Ben is being modest, between the pair of them they are well worth a visit, especially if you add some hiking in the Highlands (which I haven't done yet myself). And last but not least Istanbul - also way out of your way, but a global city that can easily take up a week on its own.