CoreAVC for Linux
If anyone has attempted to watch H.264 video on an older PC you know what a frustrating experience it can be due to the ridiculous amount of CPU the decoding eats up. CoreAVC is a Windows codec that dramatically reduces that load. Being a Windows codec we Linux users are left in the cold (we're getting used to it) – but I just discovered a project that rectifies that situation! The aptly named CoreAVC for Linux is a set of patches for mplayer, etc to allow them to load the CoreAVC codec through DirectShow emulation. Or something.
I haven't tried it out myself as I watch all my videos on my desktop, which is more than capable of handling HD H.264 videos, even with inefficient decoding. Someone give it a go and let me know if it works!