we have a great web part for doing just that right out of the box, and it's called the Content Query Web Part. This web part allows you to show items from your site based on a query, or set of rules, that you define. You can control what part of the site the web part looks for content, what types of items it returns, and it lets you filter, sort, and group those results. And, it lets you control how the items are rendered, so you can make these aggregations match the look and feel of the rest of your web site, both in what content is shown as well as how it's styled.