Here is a list of all the recognized styles of beer. If you click on each listing, it will give you a list of the top beers in that style. This should help you find the best beers for your restaurant. Remember, though, that not all beers are available in all areas. So you should also talk to your local distributors to see what they carry that will meet the needs of your business.
For example, in the American Pale Wheat style, the number one beer is Little Sumpin' Sumpin' ale, and is brewed by Lagunitas, in Laginitas California, and may well be available to your distributors. The number two beer is Oberon ale, and is brewed by Bells in Grand Rapids Michigan, and may not be available to your distributors.
At times like this your distributors will be your best guide to what they can offer outside of the "normal" beers for your area.
http://beeradvocate.com/beer/style