Oh, there are lots of nice hotels and pension in Berlin!
Here is a very original one: http://www.hotel-pension-berlin.net/en/
However, if you want to be in the hip/young scene the Choccolate Factory in Kastanienallee is a good choice. The Circus Hostels/Hotels are also well placed: http://www.circus-berlin.de
Ill see if I could get hold of a Metro map, mostly go by car these days.
Best,
Anders