Berlin (again!) and then some!

From Berlin, stop for a night or two in Dresden on the way to Prague. Vienna is on the train route to Budapest, which is your outlier. You could fly from Prague to Budapest, then backtrack to Vienna by train. From Vienna to Salzburg to Munich to Frankfurt by train.

You could rent a car from Vienna to Salzburg and take a few days to visit small towns and villages along the way, even continue into Bavaria, but back to Salzburg to return the car. Or get a car in Munich and ramble around southern Germany before Frankfurt.

Filling in the spaces depends on your travel style and interests. Do you blitz through, with 2-3 night stays or do you like to take your time and see more, perhaps at a slower pace. Are you mainly interested in the history and art, parks and museums, that big cities offer, or do you want to see more countryside and villages.

Berlin => Dresden => Prague => Vienna => Budapest is the logical order here and all very easy by train.
Night train from Budapest to Munich. Rental car to drive from Munich to Frankfurt.

David's itinerary is the most logical (all in a line with no backtracking). But following on that, why go all the way back to Frankfurt? Just fly "multi city" into Berlin and out of Budapest. If you want to see other parts of Germany, it's easiest to see them at the beginning of your trip. Fly into Munich or Frankfurt and rent a car, see Germany (working your way to Berlin), and drop the car once you get to Berlin.

Of course, you could also reverse this, starting in Budapest and going to Vienna, Prague, Dresden, and Berlin by train. After Berlin, drive around other parts of Germany and fly out of Frankfurt or Munich (or anywhere else, if you don't mind a connection).

To find these flights, use the multi city option of Kayak, Matrix ITA, etc. Don't look for two one-way tickets, as that is usually much more expensive.

Thank you all for your replies. I just got back onto this site. I though that once upon a time the site would send an email once a response was received to a post. Oh well, guess I just need to get here more often!

Chani, to answer your question. My wife and I like to fit in as much as we can. We usually walk for hours on end and take in sights and maybe an occasional museum or something. It just depends on recommendations and research. We'll probably spend maybe 2 days in Berlin this time as we were there for 6 nights last year. After Prague, Budapest and Vienna we want to explore a bit of southern Germany before flying back home from Frankfurt or whatever else works best.

Again, thank you for your replies gentlemen. Now I'm onto the planning!

If the weather is sunny, Vienna is a great city for walking, well-maintained, beautiful parks and buildings, and quiet - that really struck me last time I was there - the center is quiet for a large city. If you're there toward the end of May, the roses should be in full bloom - I was there at the beginning of June and it was only days after they'd peaked. Melk is a good day trip. Prague and Budapest are both interesting. I'd allow at least 3 full days in Prague, 4 in Budapest.

"I though that once upon a time the site would send an email once a response was received to a post."

You can still get this. Log in, then click on your name. Got to Edit Profile, and check "Email me when a user replies to my topics".

"Again, thank you for your replies gentlemen."

Chani is a lady, but the rest of us gentlemen appreciate your thanks!