Check out the tracklisting here:
http://www.discogs.com/Killing-Joke-The-Singles-Collection-1979-2012/release/4550079
CD 1 are just the normal versions of the songs.
CD 2 has mostly edits (shorter versions of the album versions) from the singles, eps etc. Interesting (and different to the album versions) imo are:
- The Beautiful Dead - Flexi-Disc Version (different mix, maybe a demo version)
- Jana is actually the Youth Mix from the same single
CD 3 has the "rarities", the ones different from what you may already know are and weren't previously released:
- Hollywood Babylon (Longer Intro Mix) is actually a complete remix
- Sixth Sun (Rough Mix) - Unreleased
- Timewave (Demo) - Unreleased
- Feast of Fools - Unreleased... has a part in it which was later used as the chorus for Penny Drops
- Four Stations of the Sun - Unreleased... this was floating around for years but only in pretty bad quality and was running ´too fast
All the other stuff is on the original singles, compilation albums, soundtracks etc.