Freakbro said:http://www.thebirdinberlin.com/ The Bird at Am Falkplatz 5 - excellent burger place with attitude. Honestly the best burger meal I have ever had. Definitely book though - took us 3 attempts to get in!
Just round the corner, since we initially couldnt get in there is (and was recommended by the bar girl at the Bird)
http://www.tebla.com/restaurants/berlin/asteria Asteria on Schonhauser Alle. Greek restaurant - oh my...masses of food, portion sizes are massive, most of it complimentary (No joke!) and continuous free ouzo! I left there on my hands and knees completely stuffed and as drunk as a skunk (10 - 12 shots of Ouzo + a big glass - all free) it cost ~£34 euro for 2. Salad starters, 2 x fruit platter deserts and coffee and biscuits all just given to us for free without asking.
http://www.tiergartenquelle.de/index.php/de/ Tiergarten Quelle on Bachstrasse. Spit and sawdust local tavern - good price, big portions, typical german food. Not as good as the above 2 but better than any expensive 'chain' restaurant in the centre.
If you like BBQ, head here, it's amazing:
http://chicagowilliamsbbq.de/
I quite enjoyed a chilled Sunday at the fleamarket at Mauerpark.
The view from the top of the Reichstag is amazing, but you'll need to queue for a ticket the day before!
Augustiner is good for Currywurst and liters of beer:
http://www.augustiner-braeu-berlin.de/index.html
Yaam is a pretty cool bar/fake beach area:
http://www.yaam.de/
This area was good for drinks, had a big open bar area and music playing most of the time, had a small gallary and a dingy club area that had a live band playing on the friday.
http://www.urbanspree.com/
The Brandenburg gate gate is worth checking out at night, looks cool when it's all lit up.
*Edit*
East side gallary is definitely worth a walk a long, we actually went to Yaam, then walked along the east side gallery to Urban spree. We didn't bother trying to get into Berghain, I've got a friend that goes to Berlin for Berghain semi-regularly and he said that he has found the best time to go and get in is late on the Sunday (2-4am) and even then it is risky, he mentioned that Tresor and about:blank are similar but can be easier to get into, if you do try to get it in make sure you have a backup plan and be prepared to queue for a few hours.
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There's also a bridge, where bands turn up and play music till early hours and street vendors selling beer. Looks awesome and people just hanging around like an outside pub, for life of me can't remember where I saw this, some youtube video probably.