There are lots of editors that can view large XML files, such as Visual Studio, Notepad++, UltraEdit and so on. But all of these have one flaw – they try and do too much in viewing XML. Things like coloring, expand/collapse widgets and so on.
One of the integration points in my current project is a large XML file (40MB or so), that consists of exactly two lines of text in the file – the XML header and then the actual content. No matter what XML viewer I chose, it would pretty much barf or never respond.
Instead of viewing the file as XML, I just changed the extension to “.txt” for that file and voila, now any text editor worth a darn can open it. Sometimes tools do too much to try and help, but there are always ways to fool them.