If you can't motivate yourself with competition, music, highlight reels and the general love of training, you probably shouldn't be training.[/FONT]
I'm new to the whole MMA arena, and I haven't been really training or anything for long, but I can share briefly what motivates me. I quote IronMan because a lot of that is motivation for me.
See... one of the biggest things that keeps me training... is training. I'm a ways away from being in shape, so the physical sensation (the chemical reactions) of training is blowing my mind. It's like a natural drug (that's actually good for me) that I want more of. So... my first recommendation for motivating yourself to train... is to train until you can't bear the thought of doing anything other than training.
Beyond that, when you're not training in the gym (or with other people), and you can, train with the mind. Study martial arts, study technique, study application. Yeah, this could mean watching UFC on TV, but it also means reading up all of these things or watching training videos on YouTube (just make sure you're watching someone who knows how to actually do things right).
I definitely second the "motivate with competition" comment. I absolutely love my BJJ class entirely of its own... learning new techniques and tools... but it's when the rolling begins that things start clicking more... and I find myself desperately wanting more and more time to train and learn.
That's... all I've got. I'm too new to really have more to say, though. Still... good luck!