XDocument: saving XML to file without BOM

Use an XmlTextWriter and pass that to the XDocument's Save() method, that way you can have more control over the type of encoding used:

var doc = new XDocument(
    new XDeclaration("1.0", "utf-8", null),
    new XElement("root", new XAttribute("note", "boogers"))
);
using (var writer = new XmlTextWriter(".\\boogers.xml", new UTF8Encoding(false)))
{
    doc.Save(writer);
}

The UTF8Encoding class constructor has an overload that specifies whether or not to use the BOM (Byte Order Mark) with a boolean value, in your case false.

The result of this code was verified using Notepad++ to inspect the file's encoding.

First of all: the service provider MUST handle it, according to XML spec, which states that BOM may be present in case of UTF-8 representation.

You can force to save your XML without BOM like this:

XmlWriterSettings settings = new XmlWriterSettings();
settings.Encoding = new UTF8Encoding(false); // The false means, do not emit the BOM.
using (XmlWriter w = XmlWriter.Create("my.xml", settings))
{
    doc.Save(w);
}

(Googled from here: http://social.msdn.microsoft.com/Forums/en/xmlandnetfx/thread/ccc08c65-01d7-43c6-adf3-1fc70fdb026a)