The first thing you notice about Momondo.com, a four-year-old metasearch engine based in Denmark, is the design. Unlike other metasearches, which tend toward muted colors and lots of boxes and text, Momondo hits you with bold blocks of color and big pictures. It doesn't look like any other metasearch, and quite frankly, that can be a bit jarring at first.

But enter some destinations and dates and you'll notice something else: Momondo's slick design extends beyond form and into function. The first thing you see is a price calendar, which displays the lowest daily departure and return dates for the entire month you're traveling. This allows you to easily see how much you could save by flying a day or two before or after your selected dates. You can cycle through months, and the prices adjust almost instantly. Great feature.

Another unique feature of Momondo is its speed. My initial search (Boston to Paris this May) took about as long as a typical metasearch query. But then I swapped out Paris for Chicago, and before I even clicked "search," the calendars changed, giving me a rough idea of Boston-Chicago airfares in May. I swapped out Boston for New York City, and the calendars changed again—all without clicking the search button. This cool feature allows you to quickly identify the cheapest options available, and gives indecisive travelers the ability to search multiple destinations for the cheapest fare.

Sticking with Boston-Chicago, I clicked "search." And guess what popped up: Southwest! But instead of fares, I got this message: "Southwest serves the route Logan Intl - Midway, but did not return any flights. We recommend you visit their site to check for great deals." I clicked the "visit" button, and was transported to southwest.com where—lo and behold—my dates were already entered and numerous fares were Momondo doesn't display fares but does transfer users to southwest.com made sense.

But a few hours later, and after emailing back and forth with Momondo co-founder Martin Lumbye, Southwest's fares were back on Momondo. I contacted Southwest for a comment on Momondo, but the airline has offered none. Lumbye chalked up my experience to a glitch. Either way, Momondo searches Southwest, which few, if any, competing sites can claim.

Lastly, travelers in Europe will be especially excited to find train fares listed alongside air fares. Simply search two destinations and Momondo includes available train fares in the results. This works in the U.S. as well, though obviously there are fewer train options.

Bottom line: Momondo is definitely worth a test drive. And once you've tried it out, I'd love to know what you think. Is it your new favorite site, or will you stick with what you've got? Leave a comment below with your thoughts.