For Amsterdam I stayed at St. Christophers Inn...it is in the red light district but was relatively clean, had a great bar and nightlife around...free wifi

For Berlin - I highly recommend The Circus. In Rosenthal Platz near the U Bahn. 19 Euros a night, great bar, cafe, free wifi in entire hostel, and did i mention 19 euros a night for a dorm? One of the best hostels I have ever stayed in.

I would second the recommendation for the Circus in Berlin. Good location, well-run, good stuff. It is very large. The breakfast is not included, but they do have an all-you-can-eat option.

I also really like Nathan's Villa. I stayed at the one in Krakow, but they have a few other locations in Poland and I believe Romania.