When it comes to searching online for airfare to Europe, it’s tough to know where to begin in an ever-expanding sea of travel sites. Here, in part 2 of our 2-part guide to finding the right flight online, we cover the best resources:

First stop: Matrix. This is ITA Software’s public airfare search engine, and it also happens to power many popular travel sites and airlines’ reservation systems. What you can’t do with Matrix: Purchase tickets directly. What you can do: Download a mobile airfare shopping app for iPhone or Android called OnTheFly. Use an interactive calendar to explore date ranges. Refer to color-coded time bars to compare flights at a glance.

Like Matrix, Fly.com, Kayak.com, and Bing.com are so-called metasearch engines. This means you can enter your search criteria in one place and simultaneously get results indexed from multiple engines. These sites are highly efficient, but again, you can’t book tickets directly. Here’s how the three sites are different:

Fly.com indexes just flights: its data comes from airlines and major travel sites (including discount and international flights, online travel agencies, and airfare consolidators).
Kayak.com also indexes flights—plus hotels, car rentals, and vacation packages.
Bing.com is slightly different in that it’s an actual search engine, or “decision engine”, in Microsoft’s words. Its travel search tool, Bing Travel, includes the cool bonus of offering price predictions for each fare (Is the fare likely to go up or down?)

Cheapoair.com functions similarly to the other metasearch travel engines in that results are culled from multiple data resources and reservation systems, but it’s a one-stop shop: Tickets can be booked directly though Cheapoair.com, either online or by phone, 24/7. Its also a full-service travel agency, with deals on hotels, vacation packages, car rentals, and airport parking.

Momondo.com is a great bet for finding cheap airfare to and within Europe. This Denmark-based aggregator indexes more than 450 travel sites—including major booking engines, airlines, and discount European airlines (an inexpensive choice if you don’t mind making a connection and possibly paying additional baggage fees). It also features city guides and a traveler blog.

Yapta.com will actually help you to pinpoint the best time to book by tracking fluctuating prices, and even better, enable you to take advantage of many U.S. airlines’ “guaranteed airfare policies”. According to this policy, if the price of flight you’ve already booked goes down, you may be eligible for a refund. Yapta will track the price of a flight you’ve booked, and alert you if it drops below the purchase price. Word to the wise: Refunds apply only if you book directly through the airline!

Along similar lines there’s Airfarewatchdog.com. What makes this site unique is its staff of dedicated “Dealhounds” (yes, real people!) who are literally sniffing out the fare sales for you. You pick your home airport, and then Airfarewatchdog.com will email you when prices go up or down.

Also worth a mention is InsideTrip.com. It’s an airfare search engine, but it’s unique because each itinerary is awarded a TripQuality score based on 12 criteria: security wait time; legroom; aircraft type; aircraft age; historical load factor; connect time; routing quality; lost bags rank; and gate location. In addition, it provide a FinalAirfare calculation—an estimate of bag and drink fees prior to departure.

Finally, if all of this just sounds like way too much work, consider Tripology.com. This is a free service that puts you in touch with certified Travel Specialists: By submitting a Trip Request online you’ll receive up to 3 Customized Trip Itineraries; you then select the one you want and book your trip.

Photo courtesy AMagill @ Flickr