Seasonal Eating

Seasonal eating does not require you to eat only during certain seasons and hibernate in others. It means eating fruits, vegetables, and meats (if you're eating meat) when they are in season.
So many living with nature/organic living/vegetarian/vegan/health books suggest it. But those books often don't list out what those seasons for those foods might be.

So here's a list of some fruits and vegetables to get you started (should you live in North America) for Spring (March-May):

Apricots
Artichokes
Asparagus
Broccoli
Corn
Mango
Oranges
Lettuce
Limes
Pineapple
Snow Peas
Spinach
Strawberries (more so towards the end of Spring)
Vidalia Onions

Now you may still see a food in the grocery store even if it's not on a current in-season list. Foods are grown in hot houses and different climates and then shipped in to your local store. If you look closely you'll find these foods are more expensive than when they're in their seasonal prime and they aren't as good quality-wise. So... you're paying more for a less tasty product.

To find out for sure what's in season in your state, visit Epicurious' Peak-Season Map or Eat Well Guide's Seasonal Food Guide.
Also Eat the Seasons has a list updated week by week based on your location Canada/USA or UK/Ireland.