Military Science Fiction is a hot field with strong authors.
William Keith is one of those authors. He writes under many pen names.
Writting as Ian Douglas, he has written The Heritage Trilogy.
The first three novels are now available in a single book called The Domination.
Coming out in November of 2000 is a collection of tales about Drakas
A spin off of his General Series (written with David Drake) is The Chosen
He also written several books with Jerry Pournelle. The last two books of the Falkenberg's Legion novels shows these two authors at the top of their form.
There have been a couple of books of shorts written in the Honor Harrington universe: More Than Honor, includes works by David Weber, David Drake & S.M. Stirling
John Ringo
The War with the Posleen
Patriots, a really cool book based on actions during the American Revolution, including the capture of Fort Ticonderoga by Ethan Allen and the Green Mountain Boys.
One of the classics of the field is Joe Haldeman's The Forever War
Timothy Zahn has two good entries in The Blackcollar and The Backlash Mission
Rick Shelley has several successful series, including his Dirgent Mercenary Corps books:
You can not discuss this field without mentioning Robert A. Heinlein's Starship Troopers. Do yourself a favor, read the book before you see the movie. If you've only seen the movie, read the book!
Good Reading Good Tunes