I use a secular text called History of a Free Nation, published by Glencoe/McGraw-Hill. It’s about 20 years old by now, but I don’t mind because most of US history happened more than 20 years ago. 🙂 It’s a reasonably well-written, comprehensive text. It is very evenhanded towards religions and ideologies, with an obvious and pretty successful attempt to avoid bias. My only philosophical objection is that there’s a persistent, implicit faith in progress, that humanity in general and American civilization in particular are continually improving. My only other complaint is that this textbook is just too big, including all kinds of things that the teacher has to cut out if there is to be any hope of hitting US history’s most important points in the course of a school year.
Regarding other books, I’m a big fan of Page Smith’s 8-volume A People’s History of the United States (not to be confused with Howard Zinn’s similarly-titled book). This would be useful for growing a teacher’s background knowledge more than for giving to students as supplemental reading, but a teacher will find many insights and stories to bring to his classroom.