Is there a way to add a lookup field column to display all the content types sitting at the site collection level?
The default lookup field can only get data from list/document library. So, you may need to create a customize field which will get content types for you to choose from.
on how to create a customized field, you can ref to http://msdn.microsoft.com/en-us/library/gg132914.aspx, and inherit a SPFieldChoice. on how to use SPContentTypeCollection, you can ref to http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.spcontenttype.aspx#Y562