8 hours enough time to sight-see in Dubai
If you're travelling with Emirates, go to the Emirates counter and pay about$50 for a 96 hour visa. You can definitely arrange this before-hand instead of at the airport, just contact your travel agent (or Emirates directly).
When u get out of the airport, ask a taxi driver to take you to see the sights, they know exactly where to go. Instead of letting them just run the meter, ask if they can't give u a set price for the "tour" - they're pretty flexible and there are always a ton of drivers so if one refuses, another will accommodate you - major competition to the advantage of the buyer.
The driver can usually put an itinerary together for you. Ours was:
From the airport, went to Jumeirah. On the way, saw Emirates Towers , Trade Centre, Jumeirah Mosque, Jumeirah beach, Burj Al Arab, Jumeirah Beach park, Mall of the Emirates (visited Ski Dubai ) and Madinat Jumeirah.