Every time it rains hard, my backyard floods. The house is 54 years old, but this didn't start happening until maybe the last 4-5 years or so. Who should I talk to about fixing this problem, and what is the usual fix?
Put in one of these. It's a French Drain, it is also on this sites FAQ. How do I build a French drain?
The need for a French Drain arises from a few problems, but usually from standing water in or around your home. This is caused by poor drainage, usually from clay rich soil or overly compacted soil. A French Drain will relocate the water very efficently. Link tot he question above for specifics.
If the ground has a slope you could plant more trees to prevent flooding during heavy rain.
Tree roots have been shown to increase the amount of water soil retains.