QED symbol in latex

If you \usepackage{amsmath}, the \blacksquare command will typeset a solid black square. The \square command will give you a hollow square.

The ulsy package has a few version of the lightning bolt for contradictions: \blitza, \blitzb, ..., \blitze. Just drop \usepackage{ulsy} into the preamble of your document.

Finally, as others have pointed out, the Comprehensive LaTeX Symbols List is a great resource for finding the perfect symbol for the job.

You can use \blacksquare ■:

When creating TeX, Knuth provided the symbol ■ (solid black square), also called by mathematicians tombstone or Halmos symbol (after Paul Halmos, who pioneered its use as an equivalent of Q.E.D.). The tombstone is sometimes open: □ (hollow black square).

\documentclass{scrartcl}
\usepackage{amssymb}
\begin{document}
$\backslash$blacksquare: $\blacksquare$

$\backslash$square: $\square$
\end{document}

You can easily find such symbols with http://write-math.com

When you want to align it to the right, add \hfill.

I use:

\renewcommand{\qed}{\hfill\blacksquare}
\newcommand{\qedwhite}{\hfill \ensuremath{\Box}}