Big sections of my lawn have died?
Large sections of my lawn have died and exposed the underlying dirt. Most of this area is now growing moss. It all seems to correlate to extremely shadowed areas. It seemed to expand quite a bit last summer when it was pretty wet. What can I plant that would thrive in this condition. I don't mind mowing, but I would like to reduce herbicides or other maintenance. Tall grasses or flowers OK.
Shaded, wet conditions are ideal for moss. Moss also thrives in poor compacted soil.
If you want a lawn in this area, you're going to have to address the soil compaction (soil aeration or even rototilling) and the shade (prune up the tree canopy, or even remove some less desirable trees).
An alternative would be to try growing something else that is more shade tolerant. You'll still have to address the soil compaction issue, but you won't need to deal with the trees. Some plants to try would be hostas, bleeding heart, columbine, astilbe, heuchera, bergenia, and many others.
Here are several references. On moss:
On lawns in the shade:
On shade gardening:
I would not recommend sod. Sod is usually grown in sun-drenched fields, and so the grass varieties would not be appropriate for your area. Reseeding is best done in late summer, at the end of August. Read here about starting a lawn:
Here is a handy calendar for lawn care tasks:
As for seed varieties, the Extension Service has done some research on best varieties: