One of the most effective ways to stay motivated to get to your workouts and train hard is to train with a training partner or in a group (or, in fact, working with a professional trainer!) Many people swear by this method and insist they have never trained any other way, including the all-knowing all-rulling God of bodybuilding, Arnold Schwarzenegger. Some research has also been done that proves the effectiveness of group vs solo training.
I see a very great deal of partner/group training (and have taught both small, like 2-person personal training, and large group, like bootcamps, training.) While some people are just goofing around the gym, others are working hard and are using the group training concept very effectively.
One group that I see all the time is specifically good at encouraging and motivating each other, and together they train much harder than when I see them individually. On top of that, they're training outside of the mold by using such tools as kettlebells, weighted vests, and circuits that mix in the above with cables, barbells, and bodyweight exercises. Good stuff.
One thing not to forget, however, is for the more experienced members of the training group, whether it consists of 2 people or 8, to help guide the others in terms of exercise technique, load selection, and the like. Something that seems like second nature to an experienced trainee and comes naturally will most likely not be so for a person new to working out. Learning proper technique is easier from the start than trying to learn it once the body has adapted to faulty mechanics.
So when training with a partner or in a group, watch out for each other, help each other, and reap the benefits.
And of course, don't forget about fitness professionals. After all, teaching proper technique, workout progression, load selection and intensity levels is our direct area of expertise.