For God's sake, go to Munich. Its so much fun. Do the brewery tour. After my third dark bock (they are 9.0 Alcohol by volume), things got really interesting.
I've been to those places. Haven't "Done It All", but I've seen some things.
1) Prague-
See the church (cathedral) and take a couple of pictures of yourselves on the Charles Bridge.
2) Munich-
Dachau (mentioned & detailed above)
Mike's Bike Tour - look into it. It is a great way to learn about the city.
Hoffbrau Haus
Olympic Stadium
Inglischer Gartens (check out the naked section)
Bayern Munich's Stadium
3) Greece-
Go to a nude beach (preferably with a girl you just met on the beach)
If you are only with your buddy, then DON'T go to a nude beach. Go to a TOPLESS beach.
Don't get hit by an old lady with a broom
Don't get chased down by her husband
Go to the Pink Palace (Corfu) or Ios (Ireland Over Seas)
Don't spend much time in Athens
You won't have a problem with nightlife in Germany. A good spot in Munich was this place called Salsalitos. Actually a Mexican themed bar/restaurant but tons of local German talent there for the 2 Euro Margarita happy hour after 10PM.
Berlin is awesome as well.
As for Greece, I would fly into Athens, spend ONE NIGHT and 1 night only as other than the parthenon etc, there isn't much to that city.
If you can make it, I would try to get to Ios Island as it was the biggest 'spring break' atmosphere I've ever seen. I think you would have to ferry from Mykonos though and you may not have time with only a few days.
If you can't get to Ios, just do Mykonos. Still a very solid place. Don't waste time on the ferry - book your flight months in advance and it will be super cheap. Try Aegean air.
In Athens, go to the restaurant at the top lykavittos hill. Sunset is an ideal time for this. Great cityscape. Have a few drinks. Watch the sunset Then, hit the bars just outside the plaka.
I know that it is difficult to tell from the last picture, but technically there are mountains surrounding the city of Athens. The problem is that the smog makes difficult to actually see them.
Enjoy Greece's capitol! (Just don't do it for more than 24 hours.)