There is some. Harpoon, Sam Adams, Wachusett... http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0CEsQFjAC&url=http://boston.redsox.mlb.com/bos/downloads/y2013/fenway_concessions_map.pdf&ei=PFdgU5_fLbChsATD_4CIAg&usg=AFQjCNEpxxwr9fz4AUNnYyxSPbSh8VhzBw&sig2=6_3hiW22pv5j2PsHN7j3nw&bvm=bv.65636070,d.cWc
Goose Island Honkers, Wachusett Green Monsta, Harpoon IPA & Summer were avail last week. High prices of course. Good beer avail outside the stadium at various bars too (ie Yard House). And despite what many geeks say here, there is good beer to be had at BeerWorks (Double Pale, Patriot Pils, & usually whatever Belgian type beer they have on).
Smuttynose Finestkind IPA out on Yawkey Way. But given the cost of a beer at Fenway, you're better pre-gaming at a local craft beer bar and saving your money come game time.
My friends get mad everytime we go and I won't drink light beers or bud. Still tough finding good stuff there. I'll be checking Sunday.