I am using \stackrel{<}{\sim} to stack up two symbols. However I need to lower \sim, which naturally goes above the line, otherwise <raises too. This is the output at the moment:

Any idea?
I am using \stackrel{<}{\sim} to stack up two symbols. However I need to lower \sim, which naturally goes above the line, otherwise <raises too. This is the output at the moment:

Any idea?
The amssymb package offers you \lesssim, and, as egreg comments, the wasysym package offers \apprle, which raises the tilde a little bit. Here they are, side by side:
\documentclass{article}
\usepackage{amssymb}
\usepackage{wasysym}
\begin{document}
$T\lesssim S \qquad T\apprle S$
\end{document}

The MnSymbol package also implements a \lesssim, which is a more compact variation of its amssymb homonymous (caution: loading amssymb and MnSymbol simultaneously will result in name clash).
\apprle from the wasysym package, which seems to raise the tilde a bit.
– egreg
Jun 10 '11 at 19:26
The obligatory Unicode solution:
% Just to get the needed fonts for the example up and running with Plain.
% You'd also need the mapping-files for this to work.
% For LaTeX, I think that unicode-math sets all of these up.
\def\mathfont{Asana Math}
\def\lfont#1#2#3{%
\expandafter\font\csname#1\endcsname="\mathfont:script=math;mapping=#2" at 10pt
\expandafter\font\csname#1s\endcsname="\mathfont:script=math;+ssty=0;mapping=#2" at 7pt
\expandafter\font\csname#1ss\endcsname="\mathfont:script=math;+ssty=1;mapping=#2" at 5pt
\textfont#3=\csname#1\endcsname
\scriptfont#3=\csname#1s\endcsname
\scriptscriptfont#3=\csname#1ss\endcsname}
\lfont{mathrm}{roman}{0}
\textfont3=\mathrm \scriptfont3=\mathrms \scriptscriptfont3=\mathrmss
\lfont{mathit}{italic}{1} % you could go on with \lfont{mathbf}{bold}{6} etc.
% end of makeshift font loading
\XeTeXmathchardef\lesssim="3"1`≲ % for LaTeX with unicode-math, this is already set.
$ T \lesssim S $
\bye
Which looks like:
