Eggs, milk, even jarred mayonnaise (which we know could probably withstand nuclear fallout) all have expiration dates, but what about the dried goods in your pantry? Some of the things have a "Best when used by" date, but not everything. This list of shelf-lives for common pantry items is taken from a book that my father bought me when he helped me "clean out" my own pantry. I think he was scared.

Baking

• All purpose flour - 12 months unopened, 6-8 months opened
• Whole wheat flour - 12 months unopened, 6 months opened (if refrigerated)
• Granulated sugar - 2 years unopened, 6 months opened
• Brown sugar - 4 months unopened, 4 month opened (in freezer)
• Confectioner's sugar - 18 months unopened
• Solid shortening - 8 months unopened, 3 months opened
• Cocoa - 2 years unopened, 1 year opened
• Baking soda - 18 months unopened, 6 months opened
• Baking powder - 6 months unopened, 3 months opened
• Cornstarch - 18 months

Spices - more info from ochef on spices, and note that spices last longer than herbs

• Whole spices - 2-4 years
• Ground spices - 2-3 years
• Paprika - 2-3 years (if refrigerated)
• Cayenne pepper - 2-3 years (if refrigerated)

Canned goods (lower acid foods have a longer shelf life)

• Tomato products - 1-2 years unopened
• Fruit juices - 1-2 years unopened
• Soups - 3-5 years unopened
• Meats - 2-4 years unopened (Spam, however, I would guess could last a life-time)
• Gravy - 3-5 years unopened
• Vegetables - 3-4 years unopened

Other stuff, with more info from the Washington Post

• Pasta (dried, no eggs) - 2 years unopened, 1 year opened
• Pasta (dried, with eggs) - 2 years unopened, 1-2 months opened
• Salad dressings - 1 year unopened, 3 months opened (in refrigerator)
• Honey - 1 year
• Ground coffee - 2 years unopened, 2 weeks opened (in refrigerator)
• Instant coffee - 1 year unopened, 3 months opened (do people really drink instant coffee?!?!)
• Bottled water - 2 years unopened, 3 months opened
• Jams and jellies - 1 year unopened, 6 months opened (in refrigerator)
• Peanut butter - 6-9 months unopened, 2-3 months opened

Of course, these are all suggested shelf-lives. You should always go by the date if there is one printed on the package, and certainly throw anything out if it looks or smells bad.