Is it possible to share content types across site collections without the content type hub?
You would need to create a site collection scoped feature that would create them and add them to the content type gallery if you are not going to use a content type hub. This makes upkeep much more complex, so I'd encourage the use of a hub if possible.
I think Content Type hub is best solution because even you can create content types using features across site collections, however any updates made to the content types cannot be easily propogated to different site collections.
Only CTH will give you this functionality.