One of my favorite sites to just browse around is the Bureau of Land Management Government Land Office.
When a property was initially transferred from the government to an individual, a land patent was drawn up. It gives the Legal Land Description of the property, including the portion of the township that was transferred. Use the Search Land Patents tool for this.
Next you can find the survey plat of the area using the Search Surveys tool. This will give a map of the area so you can pinpoint the land your ancestors owned. This is really useful when you look at the land around your ancestors. You might find that relatives will own some of the adjoining property.
One of these days I'm going to take a trip to find an ancestor's property.