To insert content from any page is very hard. You'll have to use screen scraping and drop parts of the page (the framework etc.) and hope the rest of the page doesn't ruin your design. I would not recommend it.

If you are talking about other pages in the episerver site you can access those page's properties and build the aggregator page any way you want. You can take into account what page type each page has and look for different properties and display them in different ways. Might be a lot of work though.

But if you focus on some important properties present in every page type (say name/heading, intro and body for example) you can do this more easily. What you're doing then is very similar to creating a listing page.

If you only need to include content from one page, there's a built in solution:
You can have your editors use the "Fetch data from" functionality. This enables the editors to create the same pages in different places in your page structure, but manage the content in one place.

 If you want to include content from several pages, you need to develop a new pagetype. And, as Magnus writes, you need to know which properties you want to fetch from the different pages :)