This is covered in many tutorials like lshort. But here's a more complete list:
\LaTeX typesets the LaTeX logo
\LaTeXe typesets the LaTeX2e logo
\TeX typesets the original TeX logo. You can often use it to obtain other TeX-based logos.
\PlainTeX typeset what their names say. These are defined in the
\LuaLaTeX can be obtained with the
- e-TeX and some other logos are available in package
- Finally, you can get the METAFONT logo with the package
metalogo package also allows you to customize the appearance of
\LuaLaTeX logos, which is useful if you use a font other than Computer Modern.
See also http://www.tex.ac.uk/cgi-bin/texfaq2html?label=logos.