Need a visa to transit trough Dubai airport?

No it like an airport, only if you need to exit into the country.

General Guideline

You can get your visa from your airline, hotel, tour operator alternative use a service like http://www.myvisadubai.com/.

Which nationalities can obtain visa on arrival?

Only Applicable to Nationals of the Countries Listed Below:

Western European Countries: United Kingdom, France, Italy, Germany, Holland, Belgium, Luxembourg,

Switzerland, Austria, Sweden, Norway, Denmark, Portugal, Ireland, Greece, Finland, Spain, Monaco,

Vatican City, Iceland, Andorra, San Marino, Liechtenstein.

North America: USA, Canada

Pacific Rim: Australia, New Zealand, Japan, Brunei, Hong Kong, Singapore, Malaysia, South Korea.