Whiskey River Saloon is really spacious and offers a great selection of hard alcohol and beers on tap. The beers are also cheap (or maybe $3 a pint is standard for Madison).
For entertainment, there are pool tables, some arcade games, foosball and these really lame electronic dart boards. The music selection is pretty sub-par, but I'd put up with it for the cheap beers.
It was pretty empty both nights that I went, though it was Sunday and Monday night of finals week so it might be more crowded on other nights. The bartenders were nice and let us stay past closing to finish our pool game.