I am visiting Berlin by the end of May for 5 days.Can you suggest a tour company for a S/S?Any museums?

Any info you can give me I will appreciate...Good coffee shops,typical central restaurants etc . Thanks!

You have gotten great answers! As I have been living in Berlin for 5 years I would add to these: Visit the botanic garden in Berlin Dahlem for half a day! In my opinion it is one of the largest and most beautiful botanic gardens. It opens in the evenings too and you then can get a cheaper ticket if you don麓t want to stay too long. (Underground: Rathaus Steglitz, then 8 minutes on foot, or U:Breitenbachplatz - 10 minutes on foot, the garden has two entrances). And there is an Italian restaurant at Breitenbachplatz, you can eat the best black (cuttlefish) spaghetti there! Hope I could help. And sorry for language mistakes, I麓m still learning.

General city tours are actually quite good. And you get around.
Berlin has alot to see and it's spread all over the city.
The museum island is worth a visit. Actually it's a couple of
museums with different topics. The Pergamon museum is
probably the most well known of them. The Brandenburg
Gate is worth a view and right across is the Reichstag,
the german parliament. They offer guided tours. Personally
I don't think it's that great. But if you like the combination of
old and modern architecture you might very well see this
with different eyes.

this would be my suggestions:
Get some comfy shoes, a small backpack with your essentials and walk, walk, walk... :-D Read a short guide about Berlin first and pick a couple of Museums that sound interesting to you. There are some great ones! Besides the great Museumsinsel with an abundance of great museums there is the one in Charlottenburg (forgot the name, darn! lol) close to the Schlo脽 (Palace) that is gorgeous.
Getting a sightseeing cruise is also not a bad idea, gives you some details about the history and the changes in Berlin throughout the last 10 - 15 years..
You can also take the bus around the city all by yourself, if you happen to land in Tegel just take the Tegel Express Bus, it will take you by some of the great sights!
5 days is a good time frame to see lots and get those calluses on your feet.. lol..
Make sure you take the elevator up onto the Alex tower (Alexanderplatz), sit down to a drink and enjoy the view of the city from above. Visit some of the outer districts like Kreuzberg and take a stroll through the Hasenheide..
Don麓t worry about coffee shops, there are tons of them everywhere, small caf茅s where you can get breakfast all day and restaurants all over the place... you won麓t go hungry in Berlin.. lol..
One of my favorite restaurants is on the Potsdamer Platz - it麓s not typically Germany but Italian and is called Essencia.. YUM!!!
Most of all - enjoy your trip!