I have some motivational techniques I could share that may or may not apply to everyone.
First, my motivation comes from negative reinforcement.. I know that if I walk out of the gym after skipping a set or half assing something, I feel like a weak piece of shit. I guess it's a warped obsessive kinda tool, but it works, and works well. My personality IMO comes from being in the Marines. I respond best to coming down very hard on myself. I know that most people probably couldn't handle something like this, but for me it works. It's gotten to the point to where if I have a shitty workout, I appear smaller in the mirror!
Same goes for diet. I stick to a very plain diet. I worry more about the content of the food rather than if it tastes good or not. I usually cook a pound or more of ground beef and take that to work plain with some broccoli and green beans mixed in. That usually makes up 3-4 seperate days for my meals right there.
Another approach I take is rewarding myself. I plan once a year to go back home to see my family. My goal is to look as good if not better than I did the last time I was home. Usually, the real hard motivation doesn't kick in until I'm 4 months out. But once that time comes, everything in life becomes second place (only for the hour before and after the gym), and all I can think about is beating last week's log book numbers. It's at this time where I like going 3 days (full body) to the gym. Only three days in the gym makes me twice as focused to destroy every muscle fiber in my body. Makes me more focused knowing I won't be in the gym the following day so I need to go balls to the wall..
Of course now I'm powerlifting, so the mirror doesn't really matter to me anymore. Maintaining muscle while increasing my strength every day is all I care about now.
BTW, I remember a thread on training music that someone made that spoke about motivation. I remember saying that different music, no matter what it is, has a very stong impact on performance. For me, it's not Slayer or anything hardcore, but rather certain songs that remind you of something bad [or good] that happened in your life. A cheating girlfriend, first time getting layed, or whatever. For example, when I was in Kuwait during the buildup, one of my buddies brought a cheap stereo that we listened to while training in Kuwait. Everyone brought with them their own personal baggage. Well, everytime I hear certain songs that were always played, it makes me lift like a madman..