was just thinking about mentioning this too! but for gods sake don't lose that little ticket they give you when you walk in the front door!
if you visit katz's you'll be right across the street from one of the best buffalo bars in the city: kelly's. not as exciting when a game isn't on, but worth a stop in for a beerski since you'll be right there.
i would also highly recommend a visit to McSorley's Tavern. it will be crowded on fri/sat nights but for good reason - it's one of the oldest bars in the city and a truly legendary place