If you have ancestors that fought in the Civil War or if you want to check and see if they fought in the Civil War then you have to try this site. It is usually a pay site but through the month of June they are offering free access. I logged on to it last night just to check it out and make sure the link worked, I ended up spending 3 hours looking around. You can search by soldier, regiment, or battles. I was inpressed by the amount of information the site contains. I search by name and it brought up the date and place of enlistment, age, regiment, ect. Then if you click on regiment it will give you the history of that regiment including the battles they fought.
Here's the link:
Once this page came up I picked the "American Civil War Research Database". I haven't had a chance to look over the other links but I will take a look tonight.