Most is in German, but with the help of Google Translate you might find some information here http://gedbas.genealogy.net/?lang=en (look / click at the yellow marked data bases at the top)
Some Catholic Church Books http://data.matricula-online.eu/en/
Bremer Passenger lists http://www.passagierlisten.de/
I would start by reading the Germany Genealogy Wiki at FamilySearch.org, HERE.
Next, I would check out Cyndi's List for Germany HERE.
For immigration, emigration, there are websites both in English and in German. Try the FamilySearch Wiki for Germany, Emigration and immigration.