Aggregator - An aggregator or news aggregator or feed reader is client software that uses a web feed to retrieve syndicated web content such as weblogs, podcasts, vlogs, and mainstream mass media websites, or in the case of a search aggregator, a customized set of search results. (From Wikipedia aggregator page)
Podcatcher - A podcast specific aggregator is usually an always-on program which starts when the computer is started and runs in the background. They work exactly like any newsreader someone would use to manage other web subscriptions. It manages a set of feed URIs added by the user and downloads each at a specified interval, such as every two hours. If the feed data has substantively changed from when it was previously checked (or if the feed was just added to the application's list), the program determines the location of the most recent item and automatically downloads it to the user's computer. Interestingly, it is estimated that perhaps only 20% of podcasts are actually consumed on portable media players; 80% are consumed on the PC onto which they are downloaded, or deleted from the PC without being listened to.[5] Some applications, such as iTunes, also automatically make the newly downloaded episodes available to a user's portable media player. (From Wikipedia podcast page)
iTunes - Mac/PC | Free
Juice - Open Source | Cross Platform | Free
MyYahoo / "My"Google (w/Google Reader) Cross Platform | Free
NewsGator (online) - Free
Bloglines (online) - Free
FeedDemon (PC)/NetNewsWire (Mac) - $29.95
Miro - Free
...there's a whole bunch more too...rss is everywhere