We often take Grayline day tours but I can't find any in Berlin. I have checked and do find city-discovery.com. Does anyone know anything about their tours or do you have another recommendation? Private tours are too expensive for us. We'll need a bus tour. I have read many negative comments about the hop on hop off bus which we have been satisfied with in other cities but there seem too be more negatives in Berlin.
Thanks

Insider tours has a day trip to Dresden that goes in a mini-van I believe. They also have a walking/cruise combi tour that might fit your interests. I don't know about the other tour companies, but I imagine they would have Dresden tours too.
http://www.insidertour.com/

Would you be at all interested in doing something using "suburban" rail and on your own to Potsdam? I assume you are interested in the two palaces and if so with very little planning and the willingness to do a little walking you can do one or both on your own.

It is quite a walk from Postdam station to the 2 castles and back. There are bus tours leaving from the station and you do not need to book in advance.

There are also regular buses from the train station in Potsdam to the park entrances and the castles. If you buy the ABC day ticket these buses are included. No need for a tour.

We just went on our own and used city buses. It was pretty easy. One of the bus tour touts in the train station directed us to the exit that took us to the tour buses instead of the city bus stop, but we sorted that out pretty quickly as it isn't a huge station.

Thanks to all of you. I have taken something from each reply and have decided that the best for us is to take the train to Potsdam, get a regular city bus at the station and do the castles ourselves. Thanks for saving us some money that we would have unnecessarily spent on a tour. Trying to figure it out myself, I had no idea if there were buses at the station or if it was a short or long walk etc.