There is a new white paper out regarding connectivity with SSIS to various data sources. These include connections to SQL Server, DB2, Oracle, Access, Excel, and other file-based database systems. There is some nice information in there.
The summary from the white paper:
This white paper enumerates the connectivity options for databases with SQL Server 2005 Integration Services and mentions special considerations that are required when using some database sources with some of the more complex transformations.