Emulation Dev Resources

Just for answering Marranus' question from the other day:
For DuoS, specifically, I digged most of the hardware hacking from the awesome documents of No$GBA, then lots and lots of playing around with DevKitPro...  also, studying how the guys from  DeSmuME made their GPU (which I must say is AWESOME!) saved lots of time... and finally, I must admit that I'm re-using lots of code from my own previous emulation projects . An extensive personal library of emulation functions stored in my laptop comes really handy...