By bus:
Chengdu -- Jiuzhaigou: See Chengdu Bus Schedule

Chengdu Xingnanmen Bus Station, a first class coach (RMB 93) leaves at around 8:00. The journey takes 12 hours, including 10 hours drive, one hour lunch and one hour to visit a Tibetan monastery. The coach returns from Jiuzhaigou to Chengdu around 8.00. It is better to buy the ticket one day before you leave. Warning: Except the lunch break, the drivers would also make two to three stopovers for visiting shops, and monasteries. Commodities sold at these shops are more expensive than elsewhere. Be careful with a monastery after Songpan, where some charming young girls welcome the tourists. They invented all kinds of stories to make people believe that the jewels sold at this monastery would bring good luck and fortune. It was heard that the monastery paid RMB100 to each driver for bringing tourists and travelers to them.

Chengdu Chadianzi Bus Station (Ximen Bus Station) has several buses dispatched to Jiuzhaigou, including one sleeping bus.

Jiuzhaigou --> Huanglong --> Songpan
When we visited Jiuzhaigou in 2001, there was no direct bus connection between Jiuzhaigou and Huanglong. The best way to visit Huanglong was to rent a minibus (for 6 persons) from Jiuzhaigou for this one-day trip. We managed to find two couples to share the minibus. Normally it should not be a problem as most individual travelers would like to visit Huanglong.

Since 2004, the Jiuzhaigou airport has daily buses connecting Jiuzhaigou and Huanglong. Songpan is close to the Jiuzhaigou airport. It is said that the bus link exists between Songpan and Huanglong. But we don't have detailed information.

A new option: by air
Jiuzhaigou airport was inaugurated several days before the National Day in 2003. It is located in Zhuanzhusi  川主寺 , 10 minutes by bus to Songpan, 2 hours to Jiuzhaigou, and 1 hour to Huanglong.
From Chengdu to Jiuzhaigou, there are 6 to 8 daily flights. Fixed Fare: Y410.
From Chongqing to Jiuzhaigou, 2 flights a day.
All flights are run by Southwest Airline and Sichuan Airline.

The new airport has buses running between the following places: (Info Source: www.57go.com)

From the airport to Huanglong or Jiuzhaigou: Departures are available for both places upon the arrival of each flight.

Airport -> Jiuzhaigou: One way Y45, 88km, 1.5 - 2 hours.
Airport -> Huanglong: One way Y22, 43km, 1 hours.

Jiuzhaigou -> Airport: Daily 6:00, 7:00, 17:30
Jiuzhaigou -> Huanglong: Daily 7:00
Huanglong -> Jiuzhaigou: Daily 15:00, 17:00