Visa....

Planning needs to start with a question in mind - can I enter the country without visa?
Vietnam law requires you to obtain the visa before you arrive at the airport. It is said to be impossible to receive visa at the airport (except of some rare cases which need to go through formal embassy procedures) UNLESS you have obtained a letter of recommendation in advance. You can apply for this through many agencies and it takes few days between the submission and receiving papers. Once you have the paper in hand you need to go to "visa on arrival" window at the airport, fill a questionnaire in two copies and attach 2 passport photos, pay visa fee ($25) and that's it, hopefully you are allowed to enter.
Various sources say that on occasions visa is refused, but this happens rarerly and I have not come accross such a case when looking up forums. As I udnerstand the process, it is much more probable to be refused if you arrive at the airport and try and enter without the recommendation. That is why embassy should get involved in that process, to avoid chances that you will be dismissed because of a bad mood of one officer. I guess since there is a yes/no decison for visa admission, statistically there must be cases where "no" decision happens. Hopefully I will not be this statistical occurence, neither you!

For my visa process I used http://www.myvietnamvisa.com/ and the guys were very helpful and responsive. The service fee is $20 which you can pay on-line with your credit card. Then wait for 2-3 days of processing. Don't get surprised when they email you with your papers and there will be a dozen of other names on it, including yours. This is normal and it is explained in the message that comes with it. You just need to print it (colour printing is preferred) and have it with you together with 2 photographs.
You can also use http://www.polviet.com/ which is also recommended by people who used it. However the service charge is higher: $30.