Matt Houghton wrote: Tokyo Dawn Labs Feedback Compressor II is in beta for both Mac & PC now. Bit of a resource hog, so more suited to mastering or occasional use in a mix - not something for every channel! - but it offers things most other dynamics plug-ins (whatever the price) don't and sounds superb.
The latest version of this one is much less resource-intensive now.
Also to add to the list (if I haven't missed them in this thread) are Vladg's Molot compressor and Limiter No6. They're both superb — alongside the Tokyo Dawn Labs one, these are probably the best freeware dynamics plug-ins I know of, and much better than many (and arguably most...) commercial plug-ins. Learning to get the best from them can take a while — but there's a button on the bottom to give you English instead of Russian labels, which helps.
• Vladg Limiter No6
• Vladg Molot