It's not too late to plan your summer vacation, but finding the best deal can be confusing. So I've got five tips to help you get the best deals online.

LAST-MINUTE DEALS

Flight, hotel and car rates fluctuate based on demand. So you generally get better prices by booking in advance.

But there are last-minute deals to be had. Airlines often cut prices on undersold flights. This is especially true on international flights, which are more expensive to operate.

The best time to book flights is Wednesday morning through Thursday afternoon. This is when you'll find lower prices and last-minute deals.

The same holds true for hotels. If a hotel has few bookings, room rates will decline. One site, www.TabletHotels.com, lets you search for last-minute deals at some luxury hotels.

BE FLEXIBLE

Flexible travelers have more options and find sweeter deals. So, search for flights to and from nearby cities.

For example, I searched for a flight from Phoenix Sky Harbor to Washington. It was $378 to fly to Dulles International. In comparison, it cost $272 to fly into Washington Reagan.

Flexible dates also help. You may get a better hotel rate simply by adjusting the dates of your stay.

SEARCH MANY SITES

Travel sites negotiate bulk pricing. So start by pricing your trip on sites like Orbitz, Expedia and Travelocity.

Sites like Farechase, Sidestep and Kayak make searching even easier. They don't book reservations. Rather, they search multiple travel sites at once.

Some travel sites offer package deals on hotels, cars and flights, which maximize savings.

Remember that travel sites don't always list flights from all carriers. So check with smaller airlines like Southwest and JetBlue. The same goes for hotels.

Double-check pricing on sites for larger airlines and hotels. They may list rates not available elsewhere.

Certain rates may not be advertised online at all. So call hotels and airlines to check rates. You may even find that a hotel room has vacancies not listed online.

HISTORICAL DATA

It can be tough knowing if you're getting a good deal on a flight. But you can check historical averages at sites like Farecast and FareCompare; just enter departure and destination cities and travel dates. The sites will even help you decide whether to buy or wait.

WATCH PRICES

Some hotels and travel sites guarantee their prices are the best online. That means that if your itinerary or room reservation is identical on another site with a lower price, they will match the price. The competitor's rate must be listed online.

Guarantees promise to at least match the lower price. You may also receive a further discount or a voucher. But many of these guarantees expire within 24 hours of your booking.