Just done a few days in Berlin, flew BA with on a very good service, best advise is fly to TXL as it is closer to the center of the city, (I think Air Berlin and BA ops there,there may be a few others), the alternative is easyJet to SXF a fair way out of town (it will cost about EURO 30 as opposed to approx EURO 15 from TXL)
Other than that its an exciting place to visit, stayed at the Steigenberger Hotel which is in the Mitte section of town, or if you are mainly interested in recent history look for a place to stay (if overnighting) around the Potsdammer Platz area as this is very close to the Brandenberg Gate/Tiergarten (Victory Column) and the Reichstag.
Taxis are plentiful and there is a very good public transport system in place, drinking is cheap (bottle of Becks Euro 2,60 or for a Grosse Pils Euro 4 to 5,50 depending on where you drink), if you stay in the Mitte section of the city I recommend the Gecco Bar.
Also plenty to see apart from the above there is the Berlin Zoo which I am told is very good.
Hope this helps
Bluejay