In arriving in Venice by train in October 2012, I chose the Hotel St. Lucia, within easy walking distance of the train station. It's a one-star, but was good in every way given that hotel class. A 15-minute walk from St. Mark's Square, but easy access to a vaporetto stop at the station, and also a great nearby opportunity for a gondola ride through some of the back canals. It's a small place that can book up quickly. Look for their website if interested.