Loser from InternalReality.com has released ELF2PBP v0.3 (updated from the previous ELF2PBP). This tool takes an ELF file compiled for PSP and "converts" it into a PBP file, and you can then copy this PBP file to a subdirectory in "PSP/GAME" on your Memory Stick (eg to "PSP/GAME/APP1/EBOOT.PBP"). This tool has been designed so that you could run it at the end of your makefile, you could even set your makefile to then copy the PBP to your PSP after making it (assuming you first set your psp to USB mode). Let the PSP Dev begin!
It's important to NOTE, according to the source code this utility is currently geared towards the older (JAP) PSP v1.00 firmware, however, all the newer PSP units contain v1.50 (encrypted). A source has let us know that it is feasible to re-flash your PSP using the legitimate (but difficult to locate) v1.00 firmware... but at this time it's not recommended doing so unless you REALLY know what you're doing. Stay tuned for more info soon on this topic!