Vietnam is one of those countries that does not provide visa on arrival to anyone. Well, technically it’s a visa on arrival but you need to get prior clearance from immigration. This can be done through several travel agents online and takes 2-3 days.
Please note that the pre-approved visa letter can only be used if arriving by air. On land/sea border crossings, you will need to procure a visa from a Vietnamese consulate prior to arrival. For what it’s worth, we had inquired at Phnom Penh (Cambodia) and agents there said they can process a Vietnam visa from the consulate in 2-3 days.
We visited Vietnam in November and December 2013. The visa pre-approval process is pretty straightforward although if you hold an Indian passport, some agents will not process your visa.
I found that TunTravel was willing to process a visa for Indian passport holders. They are also pretty reliable and very responsive via email. I placed the order on their website with both our passport details and had to pay USD 13 extra due to my Indian passport. :(
Each approval cost $14 and I had to pay an extra $13 so the total came to $41 for both Zara and me. (Update: As of 2018 there is no additional fee for Indian passport holders so now the $14 should cover everything).
However, once this was done, they were in touch via email and I made my payment via Paypal. Our visa approvals were processed within 24 hours without paying any expediting fee!
TunTravel emailed us our visa approval letters which we happily printed and carried with us on the flight in (we flew from Bangkok to Ho Chi Minh City). When we arrived at Ho Chi Minh airport, there was a counter for visa stamping. We approached the counter and gave our approval letters and passports. There is an ATM next to the counter (does not work most of the time, so better to come along with USD in cash). You need to pay in US Dollars for the visa stamping.
You will also need a passport photograph so make sure to carry one.
We had to pay USD 45 for each visa stamp. It took about 10 minutes at the airport to process and stamp our visa. (Update: As of 2018 the stamping fee is down to USD 25)
All in all, a pretty painless process. We were stamped with 30 day single entry visas. You can pay more for longer duration, multiple entry visas, but make sure your visa approval letter is worded appropriately.