If I had to make a list of top things that Berliners I know enjoy and recommend about the city, I'd say these are the top choices.
15. Go clothes-shopping in almost any Kiez, or neighborhood
14. Freiluftkino, or open-air cinema
13. Museums (Technical Museum, Berlin Historical Museum, DDR museum, bunker tours)
12. Go up the Reichstag to view the city and appreciate the glass dome architecture -- during the day or even at night (you can reserve times until about 11pm, I think)
11. East-side Gallery
10. Eat a Mustafa's doener kebab (totally worth the 1+ hour wait)
9. Biergartens in the park (Cafe Am Neuensee is my favorite! It's in Tiergarten.)
8. Ride your bike along the canal or from park to park
7. Party randomly until 7am (including going to a squatters flat, for a squatters' party)
6. Flea markets!
5. Kegel-bowling (traditional German bowling)
4. Go to a traditional German sauna (eg. Stadtbad Neukoelln)
2. Street festivals and open-air parties (such as Karnival der Kulturen or Mai Fest in the spring/summer time, and Christmas markets/Brandenburg Gate NYE party in the winter time)
1. (Sing at) Mauerpark's Bearpit Karaoke, in front of -- oh -- 3000 or so people at any given time!
Most of these I've done during my time in Berlin, but Geoff and I are running out of time to do the rest!! I have not had a chance to see an open-air movie here, and we've never been to a German sauna. We also haven't been to some of the recommended museums on the list. In the next week or two, this is my goal!! Chipping away at the bucket list like the best of them. Watch out!!!