PRXdecrypter can decrypt/decompress/extract:
* firmware modules from official firmwares (including some of 6.XX)
* updater modules from official updaters, including obfuscated ones
* official updater DATA.PSP
* reboot.bin and reboot_02g.bin from all retail firmwares
* EBOOT.BIN and modules from all retail games (up to 6.??), and non-retail/testing EBOOT.BIN files
* M33 custom firmware modules
* RLZ files
* KL4E files
* meimg.img and me_sdimg.img
* demos and game sharing DATA.PSP files
* index.dat
* 1SEG.PBP

Changelogs:

Version 2.3a:
- Maintenance update with the new key for 6.00-6.?? - tag 0xD91612F0 - many thanks to he who cannot be named
- Started adding some code to handle the new updater module encryption - untested, might be broken, might crash, just ignore it

Version 2.3:
- "Analyze files" option added to menu - displays info about the files without changing them
- User module keys up to 6.00, not sure if they're the ones used in the firmware though!
- Fixed decryption issue - extra data added to decrypted files
- Rewritten kernel modules for 2.XX+ allowing fewer external files and cleaner code
- Rewritten handling of compressions - 1.50 has RLZ with the correct file, 2.71 to 3.80 have RLZ, 3.80+ has KL3E, KL4E and may have RLZ depending on the exact firmware version