I tend to think of all the good things that come with a good, strong body, such as female attention, confidence, and increased physical ability. I also tend to think to myself that many things in this world require a good physique. I know that it's not true, but it often helps me get through those last five bench presses.
For example, as I'm performing the movement: "You want that Ferrari 288 GTO/beautiful girl/reputation? Then go get it, you pussy!"
Oh yeah, beating yourself up mentally helps as well. Helps motivate you to get yourself to where you want to be.
Media, especially music, helps a lot. If I see a music video full of gangsters and tough guys, and the music is good as well, it makes me want to get that sort of lifestyle, part of which requires a good physique. Even if you're not watching the music video, those images stay in your head and you are reminded of it all while exercising. Here's an example of what I'm talking about:
http://www.youtube.com/watch?v=8NTeUAmhrZs
Multi-tasking during exercise helps. I watch Law & Order: SVU while I work out. I can't really do that while I go jogging, but if you have an MP3 player, you can listen to some of that music I mentioned earlier. I prefer to just enjoy the cool, quiet morning.
My own exercise routine consists of an hour-long workout everyday, with barbells and dumbbells. Also, a one kilometer run around the block every morning.
Good luck, I hope I helped.