Concordia Hotel

The Concordia is a four star hotel and boasts that it's the only hotel overlooking St Mark's Square. That is true - although it overlooks a small corner of St Marks Square not the main square, but it is opposite the Basillica.
The entrance is round the back, which took a while to find, but once in, it's clean, friendly and welcoming. We got a free cup of tea and a selection of Venetian biscuits on arrival which was very nice. The staff are very helpful and the location is fantastic.
One draw back is that our room was on the other side of the hotel from the square - a bustling little street that is rather noisy. Also, the bells on the basilica chime at midnight for some strange reason and there's no double glazing to keep the noise out. The shutters, however do keep the light out very effectively. The beds were a little hard for my liking, but that's a matter of taste.
Breakfast was a buffet with a large choice and plenty of it.
If you go to Venice, my personal favourites were the Peggy Gugenheim Collection and the Ghetto (and Jewish museum/synagogue tour). The ice cream is fabulous and the restaurants somewhat overpriced.