Bo Johansen of Denmark has released CineGobs Spill Suppression, a free AE filter for Windows. It's "simple effect plug-in(8/16 bit) that enables you to remove spill from red, green or blue backgrounds. I think the result looks better than the standard spill suppressor included with After Effects. For more advanced control this plugin is able to create an alpha matte, based on the areas where spill is detected. Using that matte f.inst. as a track matte, you can replace the spill with the contents of another layer."
He's also released a 32-bit capable cross-platform version in Pixel Bender format for AE & Photoshop CS4, CineGobs Spill Suppression Pixel Bender. He cautions that the PB version is less user-friendly than native AE filters (every parameter is a number/slider) and slower except in 32-bit.
...via the The DV Rebel's Guide Rebel Cafe.