aw shit, this is a big deal, dude!
When I start losing motivation that this website will ever go anywhere, I just take a look at the competition that steels my ideas and seems to be more successful at using them than myself (*cough* kustomfitnessonline.com is total crap) then my lawyers calm me down a bit, and I go into an angry programming-frenzy and dish out some new stuff and put out a few new ads for it.
You need
A. a really good reason to be competitive (an old rival maybe?)
B. a new style of working out.
The best exercises are those that you've never done before. Sometimes when I feel like I'm losing interest in my workouts, I will see somebody doing an exercise that I just really want to try and then next thing you know, I'm writting a whole new routine to incorporate it into my schedule.
Try higher intensity workouts by reducing the rest time between sets (if you can do so reasonably in your workouts) ...maybe try a full-body workout with lots of super sets (just be careful not to go overboard on that one). Do those combination exercises that involve so many body parts. Try stability training. Or do body weight exercises for a week. Take your training to a different gym or a different place.
You could benefit from a training partner, but preferably somebody who is better than you. I usually feel more motivated when I training with somebody who is better than me because it shows you your potential for improvement. That person being right there training with you shows that if you stick to it you can be that good too.
Watch an action movie that gets you really pumped up and makes you want to work out for some reason. I have absolutely no clue why, but after I saw Batman Begins, I wanted to go to the gym. I know the abs on the batman costume are made out of rubber LOL, but for some reason I just felt like a good workout. There is a new batman movie coming out...

Or maybe watching some video clips from this race you want to be in could get you psyched up for it again.
And think back to the reason you started training in the first place... your very first trip to the gym, what was that about? Keep that in mind all the time.
Lastly, I hate to mention this because it goes against my personal theories (also, I'm not sure how safe it is), but in a state of emergency... they do make supplements for this sort of thing and they aren't
all un-natural. But save that for a last resort.
Good luck man!