Huatulco International Airport (HUX) is only a 15-20 minute drive from the resort areas, making for an easy experience coming and going. The facilities at the diminutive airport are modern and comfortable. The lack of flights to Huatulco from the US and Canada has been a sore point among local business owners. Things seem to be improving since AeroMexico picked up most of the defunct Mexicana's routes and now offers a domestic leg from Mexico City on AeroMexico Connect. Interjet and AeroMar also offer budget service to Huatulco out of Mexico City, though Interjet is much faster and preferable. Interjet is not linked into US and Canadian booking networks like AeroMexico and AeroMar, though, and tickets have to be bought directly from their website. At any given time there are various charter operations too, but their service is too inconsistent to warrant mention here.
Continental flies daily nonstops from Houston to Huatulco from Dec 18 - mid April. The rest of the year they pretty much only fly on Saturday, sometimes on Wednesday.
Interjet has a couple of flights a day from Mexico City to Huatulco on a regular jet as does AeroMexico Connect, and AeroMar flies turbo props that take 45 minutes longer
Rental cars are available at the airport from Thrifty, Advantage, Hertz, and Europcar. Make a reservation online and the prices can be shockingly cheap, as little as $130/week. The problem is they're not likely to respect the rate, or they will load on so much mandatory insurance that the price goes to $300-400 a week. A better option in Tangolunda is Oaxaca Rent-a-Car, which has set rates with everything included, usually cheaper than the airport rental places.
Just as it is at most airports of the world, taxi service from the airport is a racket - the taxi concession that has exclusive rights charges $45. (That's for the whole car. Don't let them try to charge you $45 per person.) Taxi service to the airport, on the other hand, is only around $12 from any cab in town. Once you're in town, taxi service is surprisingly cheap to get you on short trips around town. Anywhere in La Crucecita, and between La Crucecita and Santa Cruz or Chahue, is 20 pesos ($1.60). Between La Crucecita and Tangolunda is 40 pesos. For more extended trips, the prices get a lot more expensive.

For those coming or going around Mexico by bus, the very modern bus station is on the north side of La Crucecita on the main road into town. Buses leave here for just about anywhere you can think of in southern Mexico.