I haven't been to a game in a few years since I moved, so some of this might have changed...
When I didn't live in the neighborhood, I'd park for free on Normal just south of Pershing. The street would usually fill up down toward Root street on a weekend game, but you could park right next to the factory on Pershing and Normal most of the time.
Also, Cobblestone's on Pershing and Parnell used to have a deal where they'd let you park in their lot for $10, which could be used as a credit toward your food and beverage purchase with them.
Curious to know if any of this info is still good, as I'll be back in Chicago in September and might try to catch a game while I'm there.