Remember: Even with this list in mind you should also consult your doctor. Keep in mind your destinations and type of travel. Also realize your own personal level of paranoia. Peace of mind is worth a lot.

The Usual Suspects (These are vaccines you should already have. But be sure you're up to date):

Measles-Mumps-Rubella (MMR)
Tetanus
Chickenpox (Varicella)
Polio

Next Level (These are still fairly common and definitely needed for travel):

Hepatitis A
Hepatitis B
Typhoid
Yellow Fever (Important: you need this vaccine to get into some countries. When you get it ask for a yellow book. No this isn't code, it's the proof.)

The Serious Shots (Consider these depending on your destination and type of travel):

Japanese Encephalitis- You should consider this if you'll be in Japan over a month or if you'll be visiting rural areas in Japan or spending a lot of time outdoors.
Rabies- Crazy expensive but also a crazy scary disease. Talk to your doctor about whether this is right for you (how's that for opting out of telling you not to get it and getting sued?).
Malaria- See Rabies. There isn't a vaccine for Malaria so you have to take pills. We'd advise the daily pills since those have less severe side effects. The weekly ones can make you go kookoo. And we're kookie enough, thanks.

We ultimately opted out of the Serious Shots. Reason being: Our Japan trip doesn't qualify as high risk; Even with the Rabies vaccine, you still have to go to the hospital. And for Malaria, we go back and forth but for now are opting out. Not only are Malaria tests and cures reasonably cheap, contracting the disease very rarely fatal. Just stay very wary of flu like symptoms and take those tests like a cray.