The Cheapest Days to Buy Certain Items

Airplane Tickets

When to Buy: Wednesday morning.

Why: Most airfare sales are thrown out there on the weekend. Other airlines then jump into the game, discounting their own fares and prompting further changes by the first airline. The fares reach their lowest prices late Tuesday or early Wednesday.

Books

When to Buy: Thursday.

Why: Price compare between major chains Borders and Barnes & Noble. The former releases its weekly sales and coupons on every Thursday; the latter, every Tuesday.

Cars

When to Buy: Monday.

Why: Car dealers live for the weekend, which is when they make most of their sales. On Mondays, the low foot traffic makes it seem like the weekend will never come. That dealer desperation, paired with fewer consumers on the lot, gives you more negotiating power.

Clothing

When to Buy: Thursday evening.

Why: That's the day when stores stock their shelves for the weekend, and when many retailers start their weekend promotions. You'll find great prices and the best selection. 

Department  Store Wares

When to Buy: Saturday evening.

Why: Department stores have a lot to mark down for their Sunday circulars, so they frequently start the process on Saturday evenings before store closing, says Finney. 

Dinner Out

When to Buy: Tuesday.

Why: Most restaurants do not receive food deliveries over the weekend. Food is freshest early in the Week.

Entertainment

When to Buy: Wednesday.

Why: Plenty of movie theaters, amusement parks and museums offer extra discounts to consumers who visit midweek.

Gas

When to Buy: Thursday, before 10 a.m.

Why: The price of oil isn't the only factor influencing costs at your local pump. Prices usually swing upward on Thursdays as travelers fuel up for the coming weekend. By hitting the pump before 10 a.m. (when many station owners change their prices), you'll beat the rush and the price jump.

Groceries

When to Buy: Sunday — or Tuesday.

Why: Maximize savings by combining store sales, which run from Wednesday to Tuesday, with the latest round of coupons from your Sunday paper.

Hotel Rooms

When to Buy: Sunday.

Why: These employees are open to negotiation, he says. They'd rather have a booked room at a discounted rate than an empty room.

SmartMoney.com