Apart from the cross platform feed readers, you can try these ones on Mac OS X:
PulpFiction is a next-generation, easy-to-use, powerful RSS/Atom feed reader. Featuring a familiar Mail-like interface, PulpFiction will fetch, organize, and display news and articles from thousands of weblogs and websites. Leveraging Mail's familiar interface and ease of use, PulpFiction throws some serious muscle behind your news reading. Powerful, flexible filters move, mark, and process articles. Flags, sounds, and dock icons alert you to new or important posts. AppleScript support allows you to extend PulpFiction to work with your entire digital hub: Mail, Safari, the Finder, and more. [Price: $25, Free lite version also available]
NetNewsWire is an easy-to-use RSS and Atom newsreader for Mac OS X. Its familiar three-paned interface—similar to Apple Mail—can fetch and display news from thousands of different websites and weblogs. There is also a free lite version of NetNewsWire, that doesn't include some of the advanced features of the commercial version. [Price: $24.95, Free lite version also available]
Vienna is a freeware, open source RSS/Atom reader for the Mac OSX operating system. It provides features comparable to commercial newsreaders but it is both it and the source code are freely available for download.
Snownews is a text mode RSS/RDF newsreader. It supports all versions of RSS natively and supports other formats via plugins. Runs on Linux, *BSD, OS X (Darwin), Solaris and probably many more Unices. Yes, even works under Cygwin.
Raggle is a console RSS aggregator, written in Ruby. Features include customizable keybindings, basic HTML rendering, HTTP proxy support, OPML import/export, themes, support for various versions of RSS, Screen support. browser auto-detection, and more. Raggle has been tested under Linux, FreeBSD, Mac OSX, and OpenBSD, and should work properly under other Unix variants as well.
Shrook is a next-generation news reader that is not only easy to use, but offers advanced features not available to Mac users anywhere else. Among other things, features online synchronization and notifications to Growl. [Price: $24.95]
NewsMac is a versatile RSS news aggregator with Palm and iPod synchronization. Also available in a "pro" version. [Price: $24.99, Free lite version also available]
RSSBean is a mini RSS reader which is implemented as a Dashboard widget. Compare to other full featured RSS Reader applications, RSSBean intend to be a much simple, lightweight one with features like "auto scrolling".
NewsFire is a very simple news aggregator with "RSS with style" as a moto. Elegant but not highly usable for power users. [Price: $18.99]