Database Migration

1) What is the best option to move production OLTP and Datawarehouse Oracle databases from one location to another.

Can some one suggest a best option to migrate with minimum down time.

currently databases are hosted in a virtual server. Aim is to move databases just as it is. There are various versions of databases starting from version 8 to 11g

What I ment here is to move database from one server to other. To be more precise from US to Canada.

All most all the databases are on virtual machines. So I have a question here.

Will it be good to shutdown the virtual host and then take a backup of the virtual host. Bring the backup over here either through sneakernet or over network. Then restore the backup of the virtual host. By this way if the virtual host is restored
properly we can up the database.

We have an 8i database as well in our list. Could some one shed some light to migrate that as well.