AT&T Park has a lot of good choices. Anchor has a pavilion in center field featuring their beers and spirits from Fritz Maytag's distillery. There are a lot of other choices at the various stands and wines by the glass as well. Nothing like that Safeco Field list, though.
Wrigley Field is locked into Anheuser Busch, so the best you can hope for is some Goose Island beers. I've seen reports of Matilda on tap, but haven't seen it. The Chicago beer scene is booming, so it's too bad they can't find some space to highlight the locals. US Cellular is supposed to have better choices, but that would mean you were at a White Sox game
I was able to get an Old Style at a game last Friday. My other choices were Heineken, Corona, and Stella. In the stands you can get Bud, Bud Lite, Green Line, and 312. I'll take the Old Style all day long.
I don't think I'd trust the taps at Wrigley for a Matilda. But I might.