A great way to experience the beauty of Venice and arguably the best way to arrive in the city is by vaporetto (water bus). They leave from the airport and you can buy tickets in the airport or on the bus. You'll see the signs saying Water Bus leading down to the dock as you leave the airport. It is about a ten minute walk with luggage. Make sure you take one of the big yellow and white boats - the small wooden ones are the taxis.
Pros: Affordable and you'll get some stunnng photo opportunities too.
Cons: Takes an hour and you will have a bit of a walk to your hotel from the nearest bus stop.
Buses run from right in front of the airport and you can buy tickets in the arrival hall. The two buses to look for are the #5 run by the ACTV company or the #35 run by ATVO. They cost around 5 Euros for a one-way ticket and they drop you off in Piazzale Roma which is near the Venice train station.
Pros: The quickest and fastest way to get to Venice
Cons: Unless you're staying near Piazzale Roma you are in for a long walk or you'll need to take a water bus or taxi for the last leg to your hotel.
You get the taxis from the same place as the water bus. The don't have meters so they'll quote you a price. Best is to book online before you arrive so you don't get any nasty surprises.
Pros: They take you right to your hotel and the trip is a beautiful experience.
Driving down to the Veneto (here's our regional guide) is a very good option, if you live in Europe of course; it gives you the freedom to explore the small towns of the interior and to discover the beautiful countryside
However, if you are only visiting Venice and maybe the other main Veneto towns like Verona and Padova don't bother - you can get between cities by train easily enough and in the cities you don't need a car. You can't drive in Venice anyway :-)