The Temboz RSS aggregator is a very nicely made aggregator in Python. It uses the Ultraliberal Feedparser for parsing and can import OPML. I find the interface nicely designed and the administration quite straightforward. And it has some nice features like the two-column layout and the fairly simple integrated filtering capability as well as quite useful feed list sorting options. I'm playing around with it a bit right now - even if that will probably reduce my motivation to write my own aggregator.