I was in Vancouver for just over 48 hours - for one day, I'd recommend seeing the downtown, Stanley Park, maybe the DTES (east of Cambie, if you are into urban grit at all, next to both Chinatown and Gastown), and see some of the neighbourhoods, like Katslano, Broadway (Cambie to Arbutus is rather nice). I stayed at UBC, was quite cheap, and gave me the excuse to ride the trolley buses through some of the neighbourhoods. If you're a transit geek at all, do ride the Skytrain into Surrey across the Fraser, and get the front "railfan" seat.
On my trip, I also did the Lynn Canyon Bridge (the free one, a bit further out than the more famous Capilano [sp?] Bridge, and walked through Stanley Park, did the West Coast Express and saw many neighbourhoods, mostly by hopping on and off the trolley buses.
Vancouver's easy to get to from the airport - just buy a Translink daypass, which covers all fare zones. There's a bus that runs quite frequently through the airport that connects to the 98 B-Line up Granville to downtown.