I moved away a good few years ago, and haven't visited for a couple, but would suggest:
The Beer Engine, London Road (near Bramall Lane)
The Fat Cat, Kelham Island (There's a good few pubs there)
Hallamshire House, Crookes (Thornbridge-owned, lovely pub with snooker table)
The Grapes, Trippet Lane (Best Guinness in the city and the greatest Landlady ever)
Sheffield Tap, train station (You don't really have to leave here, never used to complain about a delayed or cancelled train)
The Bath Hotel, Victoria Street (a backstreet boozer with a fantastic beer selection).
Enjoy, very jealous. Sheffield is for my money the best drinking town in the UK. Being so compact means you can easily walk everywhere.