Campus Martius also offers free public Wi-Fi access, so you can browse B$ while you're waiting for the movie to start
There's just a couple dates left, sorry didn't post this earlier, guys, there is so much other free stuff in Detroit too, easy enough to find out, but perhaps some are lost, so here's a helping hand
http://www.downtowndetroit.org/ddp/calendar.htm
That link has a number of free events, including those at Hart Plaza, GM Ren Cen, etc....