Pipes

Pipes really does allow you to "aggregate, manipulate, and mashup" the web. This tool is so powerful its hard to even begin scratching the surface. Create aggregated rss feeds for... goods or housing in your area, news from around the web, price alerts from auction sites, and anything else you can think of! If you ever wanted to dabble in programming, but didn't want the code thing to get in the way, here's your chance.

From the site:

"Pipes is a powerful composition tool to aggregate, manipulate, and mashup content from around the web. Like Unix pipes, simple commands can be combined together to create output that meets your needs:

* combine many feeds into one, then sort, filter and translate it.
* geocode your favorite feeds and browse the items on an interactive map.
* power widgets/badges on your web site.
* grab the output of any Pipes as RSS, JSON, KML, and other formats."