What's in Dog Food?

Does anyone have a site that lists and explains all of the ingredients that are put into dog food? We are looking to switch Spencer over to a new food and would like to do our research first.

Also, if you have any suggestions for what brand you suggest, that's is great too.

Here is a sticky here that has some: http://www.pets.ca/forum/showthread.php?t=13203

Here are some very good brands.

Wellness
Innova
Chicken Soup for the Pet Lovers Soul
Solid Goild
Eagle Pack Holistic(My dog is on this)
Canidea