Rather than paying a fortune for a gondola, take vaporetti - you can buy a 1 day ticket http://www.venicewelcome.com/actv/vaporetto.htm - and a traghetto which is a public service gondola that crosses the main canals if there isn't a boat connection! You have to stand too which makes it more fun! (http://italy.worldwide-accom.com/ven...e#.UZqfXtiFJPU).

If you can get across to the island of Giudecca (just opposite St Mark's Square) you get a great view of the famous waterfront (a there and back on a vaporetto will do fine). Also climb the Campanile (bell tower) for a phenomenal view of Venice from the air.