Oh boy. I live for talking about this.
• Music. 95% of my ideas come from music. Metal music to be precise.
They live in the guitar riffs and solos, when that tasty lick hits, then I get a flash of an image. Then the lyrics develop the idea further. I listen to a lot of music, because that's where all of the ideas live.
•As I mentioned before, the idea is sparked by the music. Now...Dragon Sparking was in development hell for around 10 years, and I kept fumbling around due to life getting in the way. But the music kept me thinking about Dragon Sparking.
In particular I must shout out Dragonforce. Without that band, Rip as a character would not exist in the form he has now. Their music shaped his personality, fighting style, and appearance. Listening to their music was the place I could get full images of who Rip was. There was something about the guitars that brought him to life...and a buzzing sensation I'd get in the back of my head, just past the temples, that's when I knew the music had brought a character action to life.
Going even further in, the bands Iron Savior, Freedom Call, and Dark Moor all pushed those images further. Rip is a child born of Power Metal, and without it he wouldn't exist as he does now. Not only that, whenever I felt like quitting, their music brought me right back into creating the DS world.
Additionally I use musical sections to craft my fight scenes. I get strong mental images that show me the movements, facial expressions, and emotional outbursts.
One additional thing I use is Wikipedia mythology lists. I'll read down the list without clicking anything and just use the blurb to come up with ideas. While listening to music of course xD
•Idea hording...not really? I'm kind of a flash in a pan, where if I don't use the idea almost immediately, it's gone. At most I'll do a quick doodle to remember it, other than that, I just write in the moment into the comic. I don't often have ideas about anything else other than Dragon Sparking. If I do, it's assimilated into the DS Multiverse I plan on creating over time.