The CARA 10 minute groups are usually huge, but they're pretty organized, so if you like running with large groups go for it. They follow the Hal Higdon plan and typically have 3 different schedules for beginner, intermediate, and advanced. The Saturday or Sunday group runs are the only official ones, with I think an optional Wednesday for whomever shows up.<br><br>
They also just starting last year have a huge 20 mile run that covers the entire lakefront that I think is probably the coolest thing to happen for the Chicago running community since I've been running, but if you are not part of a CARA group, you can always just pay for it.<br><br>
If CARA doesn't sound good for you, you might want to also check out Chicago Endurance Sports. I know people that are happy with that program and think it's better organized than the CARA one.