I have been preparing for some alien invasion wargaming and the best way to do that is to read War of the Worlds by HG Wells. It is the granddaddy of all alien invasion books. This book is a sort of updated and revised version.
War of the Worlds, New Millennium by Douglas Niles takes place in 2005. The Martians invade Earth with updated technology and it flows from there. In some ways this book does for the HG Wells story what the George Pal WOTW movie did in the 1950s. It is less of a techno novel than I would have liked but there are some good wargame scenarios in the book.