My recommendations:

Alma Highland Festival, Alma, MI
http://www.almahighlandfestival.com/

Ohio Scottish Festival, Wellington, OH
http://www.ohioscottishgames.com/

Detroit St. Andrew's Highland Games, Livonia, MI
http://www.highlandgames.com/

Detroit is actually August 4th, so you can still make that one if you like.
Also, if you're willing to drive a bit further, the Chicago games are a lot of fun too.

Chicago Highland Games, Oak Brook, IL
http://www.chicago-scots.org/


There are a lot of others too, most pretty small, but those I've found the best in those three states to spectate at. The Canadian games are a lot of fun too, there are some in Sarnia and Chatam that aren't too ridiculously far out that are good to go to.