Macintosh Software
Here are some links for Apple Macintosh in general. For OS X specific stuff, go here.
You can download some older (and current) system software from Apple.
iTunes and Apple's music store
Database: 12,000 items of Mac-compatible software and hardware
Matt Neuburg: some links for hypercard, realbasic, frontier, software reviews, etc.
This guy's favorite software conveniently categorized
Serial port and X-10 scripting additions
Compression, Encoding & Disk Images - a big list