The Nuclex Framework contains a content pipeline extension, Nuclex.Fonts.Content.TrueTypeImporter.dll, which acts as a replacement for XNA's built-in font processor. It can create SpriteFonts that are compatible with those created by XNA's own importer and it can create VectorFonts which can be rendered in various modes (outlined, flat-filled, extruded) by the Nuclex.Fonts library.
Sprite Fonts (2D)
SpriteFonts created by the Nuclex content pipeline extension can be used like any normal font created by the XNA content processor, but they look a bit different because the character bitmaps are created with FreeType, an Open Source font rendering engine, instead of Windows' own text rendering API.
Text will also be centered on the text's baseline (that's the line letters like 'abcde' sit upon and letters like 'gjpqy' go below), which is (in the eyes of this writer :P) more useful than positioning text by its upper left corner.
Vector Fonts (3D)
VectorFonts store the interpolated vertices from the curves making up a character and thus allow text to be rendered in full 3D. Supported modes include outlined text consisting of line strips, flat-filled text which renders only the faces of letters and extruded text, which renders letters as fully sealed 3D meshes.