I draw inspiration from many things. Mostly stuff that's happened within my circle of friends over the years. When I first started messing around with RM2K back in '02, the aim was to actually make a comedy RPG based on what we got up to during our school days, only greatly exaggerated. Some of these elements are still planned for my current XP project.
TV programmes and other games/RPGs also give me a lot of inspiration. I actually hate it when I play a new RPG because I almost always end-up wanting to shift the setting and atmosphere to suit it. Like the time I played Digital Devil Saga and decided that my RPG needed to have a darker atmosphere and demon-morphs. I've also toyed with Lost/Heroes themes in the past, some of which are still set to be in the game.
Motivation is a big problem for me. Oddly enough, I often lose it due to being inspired by something new. More recent ideas win over against existing ones, and I end up wanting to change almost everything around. Sometimes I'll spend weeks designing characters/animations, jotting down ideas, and really getting stuck in. Then all of a sudden I'll look back on what I've done and just not like any of it. I've made attack animations in the past which I've been immensely proud of, yet when I play them now I just think "ugh...what was I on when I made this?", and leave the whole project alone for the next few weeks. I think it's just a case of my spriting skills getting better over time, and no longer being satisfied with what I already have. Right now I'm in the process of completely redesigning 90% of my playable cast, and cutting almost every skill animation I've made over the last year or so. Although I'm confident that this really will be the last redesign...
On a positive note, it usually only takes one tiny, often insignificant (in the grand scheme of things) idea to set me off again.