I recently posted about my need for a simpler RSS aggregator.
I worked through the massive list of existing RSS aggregators at wikipedia and couldn't reallly find something that did exactly what I wanted and worked.
I needed something that was simple, cached hourly, displayed various encodings well and worked with RSS and Atom formats. Most importantly, I wanted something I could install on my own server, and it needed to be community oriented (not designed for a single reader).
Most of the existing solutions on the web are hosted by a third party, and are limited in the number of feeds that they can aggregate.
The best hosted solution I found was Gregarius, which has a lovely community. I think that gregarious will take the cake sometime this year as aggregating catches on. For now, however, the plugins are pretty limited — you are locked into a personal reader with "Read/Unread" tagging. (Which makes Gregarious a great replacement for a newsreader like Bloglines, but it's not good for a community aggregator where lots of people visit.)
If I were a better person I'd just write a Gregarius plugin, but instead I've just reworked some of Feed2JS's code (which is in turn dependent on the Magpie RSS parser.)
You can download it here.
Otherwise edit the php file with the rss or atom feeds you want to include. It will probably need a little CSS to spice things up. You can send comments or questions about the script to chris(at)nonprofitdesign.org. I'll release another version sometime soon with better documentation and a prettier front end.
UPDATE: That page now uses simplepie, which kicks ass.