Speaking of the Battles and Leaders volumes - all four are availble online for viewing and/or download, this link is for the first:

http://www.openlibrary.org/details/battlesleadersci01underich

I checked for the Selfridge tome, but didn't get a hit. The Gustavus Fox book is there though:

http://www.archive.org/details/confidentialfox00vasarich

Not sure if this both together or if it's just one or the other.

There are a ton of regimental histories and many naval memoirs and histories also. The Flip Book is quite nice for viewing online, and the .pdfs great for offline viewing.