OK I know it's 4 weeks late but here goes.
1. Getting around
Berlin is such a massive city so don't even think about seeing all of it on foot. Get a "Welcome Card" (21 euros for 3 days) and you'll get unlimited travel on the excellent U-bahn (underground), S-bahn (local trains) and local buses. All in all a fantastic, well-organised and easy to follow travel network.
2. The Wall (what's left of it)
Even if the powers that be moved very quickly to erase recent history, it's hard to visit Berlin and not be swept away by its recent past. Most of the wall is now gone, however there are two significant sections: the East Side Gallery (which we didn't see this time) and another preserved section which also shares its outdoor space with the Topographie des Terrors, an open air exhibition about the Nazis. Both of these are not too far away from...
3. ...Checkpoint Charlie
...OK so it's a tourist trap but it's also a must-see. The original Checkpoint Charlie no longer exists and has been replaced by a replica, complete with photo-opportunist 'soldiers' but the Haus am Checkpoint Charlie museum provides a fascinating way to spend a couple of hours, and details all the different methods people used to get over, under, or through the Wall.
4. The DDR Museum
So how did ordinary people spend their day to day lives in the German Democratic Republic? This modern, hands-on museum will answer that question. It doesn't dwell on sensationalism but rather the more mundane and normal aspects of East German daily life before the Wall came down, which makes it all the more interesting and insightful.
5. The Zoo
Knut's the main draw here: he may no longer be small and cute but he's a celebrity and boy, does he know it. Berlin Zoo is vast but most of it can be explored in a day. Special mention for the ape house, which I loved.
Shop till you drop on Berlin's most famous shopping street. Or at least window shop; lots of mainstream/designer stores to give you ideas of what to buy in the event that you ever get rich.
7. Food and Drink
Berlin provides an excellent choice of international eateries - you may find traditional German restaurants a bit harder to find though. For those on a budget, get your wurst from the many Imbiss (takeaway) vans all over the city; but don't worry, eating out is affordable and enjoyable. It's beer country here so don't forget to try the local ones Berliner Pilsener/Berliner Kindl.
Get a feel of the old east by visiting this part of the city which is home to the TV tower and the world clock, two essential photo opportunities which have lived on even after the fall of the Wall.
Possibly the prettiest part of the city, this recently renovated historical quarter on the banks of the river manages to look and feel authentic. Lots of traditional German restaurants here too. Decided this was our favourite part of the city.
10. Hot hot hot
Not the weather, which nevertheless was pleasant and bearable for an intensive city break, but I refer to many of the young men of this fine city, who were very visually appealing indeed. (My faithful travelling companion also said that he was equally impressed with the young ladies too.)
Edit 20.10.07: Been having a few problems uploading my pics but I'm ever hopeful that I'll work this out :-)