Suggest an Addon for pulling content from own sites

Hi all

I have a main site of which is the main blog for what i do, however I also have specific subject sites that I at this stage copy and paste from the main site to the subject specific.

Can anyone advise if there is a plugin/addon I can use on the subject specific sites that will pull posts and their content (including images) from my main site to the subject specific sites. I assume it would be done by having tags on the posts on the main site.

Not sure and hence my request – I hope you can suggest a solution for me.

Cheers