I did not go to London, but the rest I can speak to.
My first hint is to buy Rick Steves europe book. It is incredible and has so many "non-touristy" things to do and see that are phenomenal.
Paris- I'm going to preface this by advising that you stay at least 4 nights in Paris. There is so much to do. I'll try and be succinct.
-Use the metro. Their train system is one of the best in the world (at least one of the best I've ever experienced). Try and stay at a place near a metro line stop. Trust me on this one.
-If you aren't a huge museum fan then honestly the Louvre is overrated. Visit the Musee de Orsay instead. It is the impressionist museum and it is housed in an old train station. Way better than the Louvre.
-Spend a day at Chateau Versailles. It is an old French palace that is absolutely massive and very ornate. When I say spend a day, I mean set aside at least 4-6 hours. It takes about 2-3 hours to see the palace and then after you get out of the palace itself, the grounds are so expansive and gorgeous that you will just want to wander around for a while and get lost.
-Take the Fat Tire, Night Bike Tour. It was one of my favorite things that I got to do all summer. Unless you hate bikes, I promise you won't regret it.
-Check out the Montemarte district.
-Check out Sacre Cuere. It is very stereotypical Paris (to Americans anyways). The waiters wear berets and it is all cheeky and fun, but the great part about it is the amazing view of Paris.
-Go to the street Rue Cler. It is where the hip Parisian college students hang out, and it has a slew of great restaurants. Try Le Tribeca.
Amsterdam-1-2 days max. It is a very cool city and very pretty, but unless you want to smoke weed for a week, then 1-2 days is all you need.
-Walk the city. Amsterdam is fairly small, so walking from place to place there is a really fun option because you really get to take in the city and it doesn't take too long to get where you are going. We were completely on foot and it only took us about 6 hours to see almost the entire city.
-If you are going to smoke I would make 2 recommendations; smoke once in the red light district (you are in Amsterdam so you pretty much have to), and then venture outside of town and find a shop that is only locals to smoke at. Way different vibe and a pretty neat experience.
Prague-1-3 nights
-If have been on your trip for a while and are craving some mexican food, try La Casa Blu. It isn't the greatest, but it will hit the spot if you are dying for a fix.
-Bohemia bagel is a great place for breakfast (if you want to feel like a tourist). We went there every morning. You will learn pretty quickly when you are in Europe that they don't really value breakfast, but bohemia bagel will set you up with a hearty meal to start the day.
-Go to old town square and see the astronomical clock tower.
-Peddle around in the markets and grab some fresh fruit (the cherries are awesome)
-Check out the Jewish quarter.
-Go to the monastery that overlooks the city. The monks brew some pretty incredible beer there. You may have to ask around for directions, but if you look hard enough you will find it.
-There is also a Hooters in Prague, if you like Hooters.
-If you get a chance, check out Cesky Krumlov. It is a city about 2 hours from Prague that is supposedly awesome (I didn't go, but my friend says it is one of his favorite cities in the world).
Munich-2-3 nights
-Waldwirtschaft is the name of a place where the locals eat and drink. It is a true German beer garten and is awesome. We got to catch the Germany vs. Portugal eurocup game there, so needless to say, we had an incredible time.
-The olympics were held in munich once upon a time and they have all of their olympic stadium and what not in town (I didn't go, but have heard good things)
-We went to Dachau. It is very very heavy, but if you want a new perspective on the holocaust, take a tour of Dachau. It is a monument to the triumph of the Jewish people in an extremely difficult time. Very heavy, but very cool.
-In my experience, the germans were some of the nicest people we encountered. Make friends with the locals.
Interlakken-3-5 days
-Do yourself a favor and take the gondola and short hike up the mountain to the little town of Murren and stay there instead. The accommodations are cheaper, the scenery is 1000 times better, and it is very quiet. Seriously, stay in Murren. Just trust me.
-Eat the fondue at Stagerstubli. It is a swiss staple. And don't be intimidated just because the entire place smells like feet.
-It is the best city for adrenaline pumping sports in Europe (I would assume), so pick a couple of things and do them. Canyoning looked awesome, but we went too early in June and since the snow was still semi-built up we couldn't canyon. We did the ropes course instead, which was still really fun.
-Hike. It is one of the most beautiful places in the world. Just walk around.
I've got to go to bed, but I'll detail the rest later. Hope this is what you are looking for, if not then stop me so I don't keep telling you all this useless information haha.
and Prague is incredibly beautiful--walk around and take pictures. There's also quite the opportunity to party there.