You can get sunburnt in some unexpected places when you go for a ride. Putting sunscreen on in the right places before you head out can make a huge difference.
Here's a quick list of spots not to forget:
Back of the knee and calves: Your body position on a bike puts these areas under fire.
Top of the knees: The top of your knees may very well get the most sun while biking.
Back of the neck: Again, your body position on a bike makes your neck particularly vulnerable.
Forearms and Shoulders: The tops of your arms will get a lot of sun, and if you wear a tank top, don't forget the shoulders. I almost exclusively ride in long sleeves to protect my arms.
Front and back of the ears: These are some of the most commonly forgotten areas in normal sunscreen application and they can get even more exposure on a bike.
Face and Nose: Just because your helmet has a visor doesn't mean your face wont get burnt.
The Gap: An unexpected and often forgotten sunburn spot is commonly known as The Gap. The Gap is the exposed part of your back between the back of your shorts and the bottom of your shirt. Cover a few inches of your back below and above your waist.
Scalp: For the few of us who may be a little thin on the hair, helmet head is a serious concern. Modern bike helmets are designed to be so well ventilated that they provide little coverage. While the vents may look good on your helmet, a nice replica burnt onto your head is never a good idea.