I noticed not too long ago that iPodderx had gone away, so I have since removed it from the list of podcast aggregation services. It was sued by Apple and forced to change the name of their application. If it comes back, I will add it again because it was supposed to be a really good application.
I tested out another podcast aggregator called Juice, which hogged some serious resources on my laptop. It also was not very user friendly, didn't make it easy to find podcasts, etc... I have removed it from my system.
If anyone knows of or uses a podcast aggregation client or service and likes it, drop me a line at paul /at/ pauldotcom.com
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Apparently iPodderx was renamed Juice reciever. So, Juice and iPodderx are one in the same.
I'm currently investigating using FeedDemon to do podcast aggregation, which I'm already using as my news (RSS) reader. It looks promising, but I haven't had a chance to test fully.
Actually Juice is what used to be called ipodder. IpodderX hasn't gotten its new name yet if I recall. They were running a contest.
I personally use Amarok on Linux to manage my MP3's, Internet Radio stations and my podcasts. Yes it is a memory hog compared to XMMS or mpg123 but the extra functionality is more than worth it IMHO. IIRC it can also be run on OSX using FINK.
If you are using linux, try, you might just like it....