couple i know of:
controller mods
controller port led
case mod
leds (inside)
softmod - software
fan swap
jewel mod - tut
ive only done the jewel mod so far but i dont know how to do the others yet so yeah, from what ive heard they're about easy-medium solder skills, but if youve been doing psp's then you should be fine
thats what i could think of off the top of my head, theres more if you look through the xbox forum