Bob,
I'm a Shields native currently living in East Lansing. I'm also writing a guide to inland diving in Michigan that will be published in a map form next fall. If you're looking for Great Lakes sites, the Straits, Thunder Bay and Munising are my favorite. The Straits and Thunder Bay can be dived comfortably in a wet suit from June to early October and both have regular charter operators you can get on almost any weekend.
As far as inland sites, the farther north you go in the state the better they are generally in terms of visibility. However, there are some sites close to you that won't cost you $75 for a charter like most Great Lakes dives. Oasis Lake park just west of Standish and Lake Fenton just south of Flint come to mind. Haithco Park off of I-675 in Saginaw Township is sometimes diveable though visibility and depth tend to vary. If you e-mail me at bradymsu@yahoo.ie, I can give you directions to the first two sites. I'm sure you know how to get to Haithco. Give me a hollar if you're looking for a safe and attitude free dive buddy no matter what level you're at.
If you're adventerous, I'd suggest buying a DeLorme atlas from Meijers and going to lakes around the area with public access sites. You'll find bad vis at a lot of them but often you can find hidden gems as well, especially in the spring and fall. Matt at the Diver's Berth on Delta Road can also offer you suggestions. He runs a dive club in Saginaw that you may want to join. He knows his stuff.
-Brady