Fare of the Day: San Francisco, CA (SFO) to San Juan, PR (SJU) $267 RT, including all taxes on American Airlines.

Travel Tuesday and Wednesdays starting in September through March of next year.  No peak summer travel available.

Fare of the Day: Detroit, MI (DTW) to Denver, CO (DEN) $198 RT non-stop, including all taxes on Southwest Airlines.

Fare available for travel any day of the week if available, no minimum stay requirement, travel through January 5, 2014.

Fly from Chicago to New York for $214 round-trip, nonstop, including all taxes, on JetBlue.

We found seats departing ORD on October 1, and returning from JFK on October 8. Other dates are also available for spring and fall travel (no July dates), on Tuesdays, Wednesdays, and Saturdays.

For booking info, see our Fare Details.

As we've said many times, the best airfare deals are only sometimes available on the airlines' own web sites, and many of them come in the form of promo code deals and special offers. You can only get these, in some cases, if you sign up for alerts and emails directly from the airlines. However, we've noticed that many airlines make it a bit challenging to find where to sign up for alerts! So we've gathered links to most US airlines all in one handy dandy place.  So sign up and save! (Enough email already? Airfarewatchdog lists any and all promo code and special fare sales on the AirfarewatchdogBlog).

Follow Airfarewatchdog @airfarewatchdog on Twitter to get late-breaking airfare sales. It's faster than email alerts!

Usually, we're not so big on buying miles because the price per mile isn't good value. But what if your airline gives you a 100% bonus? 

Through May 31, 2013 for every mile you buy, US Airways will give you an additional mile for free.

Buy 50,000 miles for $1881 (including tax) and you get an additional 50,000. You only need 90,000 miles to fly to Asia round-trip from the US in business class, for example, on airlines in the US Airways-affiliated Star Alliance (such as Singapore, Asiana, and Lufthansa; see US Airways' partner award chart.

US Airways is planning to exit the Star Alliance following the completion of its merger with American, but the exit date is not expected until 2014. Until then, the US Airways award ticket prices are the most affordable of any domestic airline.

These miles could take you to Australia in business class for 110,000 miles (most other airlines charge around 140,000-150,000 for business class). European business class flights clock in at 100,000 miles roundtrip, and roundtrips to Africa are 120,000 miles.

One of the best ways to search for US Airways award availability is actually to use its competitor United Airlines' site, which features accurate access to most "Saver" awards. Once you see the availability on United's website, you then call US Airways and tell them the exact flights you want.

Needless to say, you'll also have to pay taxes on the "free" ticket, which could set you back another $100-300 or so, depending on your destination. And you might have trouble finding the exact dates you prefer, since free seats are capacity controlled, so it's a good idea to see what the availability is before you buy the miles. But you still come out on top, saving quite a bit on travel in business class.

Still, you could pick up a business class ticket for less than $2,000 with this method. Business class tickets to Australia can cost up to $10,000 meaning buying these miles can save you more than 75%.

You needn't buy 50,000 miles if you already have miles in your account. The minimum purchase for the bonus is 5000 miles for $188 (including tax), which makes this a great way to top up your account. However, if you have zero miles, you can still attain a business class ticket simply by buying the miles with this promotion. Note that your Dividend Miles account must be at least 12 days old to qualify.

And eventually you'll be able to transfer these miles to your American Airlines Aadvantage account when the two airlines fully merge.

You might also like: Airline Frequent Flyer Fee Chart

Tips for cashing in your miles

Frequent flyer hacks only the most frequent flyers know

Follow us on Twitter @airfarewatchdog

Frequent flyer tickets are supposed to be free, right? Well, not exactly. Airlines are socking it to passengers with all kinds of fees and penalties that take some of the joy out of redeeming an award ticket.

For example, American can kill customers with fees. Imagine this scenario: you book a frequent flyer ticket at the last minute using a reservations phone agent ($75+$25), then have to change the date of travel ($150), but ultimately can't make the trip (illness, death in the family, whatever $150): your total fees (assuming you want to redeposit the miles for future use) will be $400 without even leaving the ground!

In this same scenario, Delta won't charge you a last-minute booking fee, but if you want to change or cancel that ticket within 72 hours of travel you forfeit the miles altogether. No chance to use them again.

Note that since the four remaining "legacy" airlines (US, DL, AA, and UA) have recently upped their domestic fare change fee from $150 to $200, we wouldn't be surprised to see frequent flyer change fees to be increased as well. As of this writing, that hasn't happened (it's still $150).

Remember agents all seem to have different interpretations of the rules and fees so it never hurts to hang up and call back to see if another agent has a cheaper fee or allows you to change something for free. But, one thing is for sure, traveling for free these days ain't what it used to be!

One popular workaround is that if there is a schedule change to your flight (with Delta, they seem to jigger their timetable almost every other month), you may be able to change your ticket without a fee. Typically, if the airline changes the times of your flight (even by a few minutes), it can put connections in jeopardy or make it less likely for checked bags to make it to the final destination. So it pays to keep checking your reservation to see if you may be able to get a change for free.

Keep in mind, too, that depending on your frequent flyer membership level, some of these fees may not apply to you, or they may be lower than shown. Updated May 4, 2013.

Related: Get a 100% bonus when you buy US Air miles (through end of May 2013)

Frequent Flyer Hacks Only the Most Frequent Flyers Know

See those little promo code boxes on your favorite airline's website? What's that all about? Well, airlines are trying to get you to book directly with their websites rather than through third-party sites, and from time to time, you'll receive promo codes in your e-mail because you signed up for e-mail from your favorite airlines and online travel agencies. (Curiously, some airlines hide their email sign up, so we've included a handy chart here.)

The deals vary. We've seen Southwest Airlines offer 50% off promo codes, Air New Zealand has had $200 off codes, and so on, but the typical code deal is $10, $20, or 10-15%. Or you might get bonus frequent flyer miles by entering a promo code. American Airlines recently offered 10,000-20,000 bonus miles on a new route if you used a promo code.

These codes can only be redeemed if you book directly on the airlines' websites. How to find them? Try doing a browser search for “airline + promo code” to find mentions of these codes online, or check right here-- the Airfarewatchdog blog--where promo code deals are regularly listed, and follow our Twitter feed because we tweet them too.

Fly from Denver to Orlando for $198 round-trip, nonstop, including all taxes, on Frontier.

We found seats departing Denver on May 8, and returning from Orlando on May 14, as seen below. Other dates also available for travel only in May.

For booking info, see our Fare Details.

Yep, we've mentioned this route a lot lately, but it's just too good not to share again. And suuuurely someone in all of New York could use a trip to Honolulu this spring, right? We found seats departing JFK as soon as May 6, returning from Honolulu on May 14, for $443 round-trip, including all taxes, as seen by the screen shot below.

And yes, this is all nonstop, on Hawaiian Airlines.

For more great fares to Hawaii, visit our fare pages for Honolulu, Kahului-Maui, Kona, and Lihue.

Considering the lack of available overhead space on most flights, along with those eager passengers who crowd the gate waiting to fill it, it's a wonder more carriers haven't started charging for carry-on baggage. You may recall Allegiant and Spirit were first to take the plunge a while back, but the trend soon fizzled. At least til today, when Frontier announced that they too will charge for carry-ons on some tickets starting in summer, with fees ranging from $25 to $100.

Only travelers booking Frontier's Basic fares via third party sites will be charged. All tickets purchased directly from FlyFrontier.com are excluded from the new fee. Charges apply only to carry-on luggage, and all passengers are allowed one free personal item, no larger than 18” x 14” x 8”, for under seat storage.

No exact date yet on when this new fee will kick in, but stay tuned!