On BA, Goose Island has 163 Current and 290 Archived beers!! 453 combined. Can you find a Brewery to beat that?
Rock Bottom 363 current and 549 retired. Granted Rock Bottom does not really compare, the company as a whole is quite prolific.
Mikkeller is the Paul Erdős of breweries -- a bumblebee that goes from flower to flower, pollinating each.
While not that many iron Hill brewery has like 243 active, granted with all their locals at any given point you probably have between 60-100 on tap, I guess... Just rough ballpark #'s
See the problem with a thread like this is that a "brewery" like Rock Bottom that has 34 locations and allows their brewers room to brew their own beers, the numbers get big real quick. If you're limiting it to one brewing location that quantifies it a little more. Even GI has the 2 brewpubs in addition to the production brewery, so individual beers amass quite quickly.