I have a site collection containing sites with the same list template called Tasks. I want to aggregate all the active tasks and display them at the top level site. I think the XSLT List View Web Part (XLV) is the solution because I'm not an expert at XSLT so I don't want to use a CQWP and apply XSLT if possible. I believe that was the solution in SP 2007, but the new web part in SP 2010 is supposed to make it easier.
This article by Waldek Mastykarz describes how you could achieve that with Content Query Web Part. It's seems to be perfect for your scenario.