For Audio/Video stream rippers native to Mac OS X,
I have seen no mention of my two favorites that are also both free.
The links posted in this thread so far seem to be tables with really out of date stuff.

I would suggest the original poster check out these programs.

CocoaJT 5.2.2 and MPEG Streamclip 1.9

with CocaoJT it is real easy to download a windows media or real media video/audio stream in background using it's recorder option while doing other stuff. I just downloaded a 30 MB windows media stream today and it definitely took less time to download it than to watch it. The interface is a little funky but it works beautifully.

I should note that I am still using Tiger (10.4.11) and have not yet switched to Leopard (probably won't for a while till at least till several more updates and bug fixes occur, everything works on Tiger, no reason to break anything).