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.
\AmSTeX, \BibTeX, \SliTeX and \PlainTeX typeset what their names say. These are defined in the doc package.
\XeTeX, \XeLaTeX, \LuaTeX and \LuaLaTeX can be obtained with the metalogo package
- e-TeX and some other logos are available in package
hologo
- Finally, you can get the METAFONT logo with the package
mflogo
The metalogo package also allows you to customize the appearance of \TeX, \LaTeX, \LaTeXe, \XeTeX, \XeLaTeX, \LuaTeX and \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.
\LaTeX. You don't need a package for this. See How to write (La)TeX (with braces) or any other TeX-related logo – Martin Scharrer♦ Jul 22 '11 at 8:54