Danish ResearchSometimes your Swedes may have come from Denmark originally, married a Dane after emigration, or emigrated through Denmark. Here are some resources, generously collected by Arne Hansson on the Swedestoo list.
Arne's note: Copenhagen in Danish is "København". In Swedish, it is Köpenhamn. To use the character "ø", copy and paste it from here, if you have difficulties creating an "ø" on your keyboard.
Danish Demographic Database: http://ddd.dda.dk/ddd_en.htm
Danish digitized churchbooks: http://www.arkivalieronline.dk/ (similar to Genline for Swedish research). Both are run by the Danish State Archives. Press the button English flag to the left to get English. Both sites are free if you register.
DIS-Danmark: http://www.dis-danmark.dk/dis-english.asp - the site for Danish researchers online.
Danish Emigration Archives: http://www.emiarch.dk/home.php3