Here is a most excellant book on tree ID
Ron in Drums PA
>"National Audubon Society Field Guide to Trees"
With this book you can identify a tree by it's bark, leaves, flowers, fruit, nuts, cones or it's autumn foliage.
There are over 700 photos and descriptions for 100s of tree.
Steve, from the photo of your mystery tree, I can see why some folks think this is sumac or black cherry. According to this book, if you scratch the bark it will smell like cherry. If it doesn't it's sumac and you'll need to get some shots from your doctor.