A symbol for the quotient of two objects

How about using \left, \right, and \raisebox?

\newcommand{\bigslant}[2]{{\raisebox{.2em}{$#1$}\left/\raisebox{-.2em}{$#2$}\right.}}

\begin{equation}
\bigslant{\mathcal{O}_{(V',0)}}{\mathcal{O}_{(V,0)}}
\end{equation}

which gives

The only problem is that I need to re-enter mathmode inside the \raiseboxes. Anyone know how to avoid that?

If you want to invoke the Someone Else's Problem principle, there's also the faktor package, which ostensibly was designed to do what you want, and which implements using the AMS symbol \diagup. But IMHO the slash is a bit small.

For in-line expressions, you can also consider the nicefrac package, which makes both the "denominator" and "numerator" small.

As already mentioned, there are two packages to solve this problem:

• xfrac - typeset fractions in the form n/d generally
• faktor - especially to typeset factor structures

Here is a comparison between the \sfrac{n}{d} and \faktor{n}{d} commands which also demonstrates how they behave in comparison to normal text:

\documentclass[12pt,preview, border={2pt,2pt,2pt,2pt}]{standalone}
\usepackage[english]{babel}    
\usepackage{xfrac}    
\usepackage{amsmath}
\usepackage[amsmath,thmmarks,standard]{ntheorem}
\usepackage{faktor}

\begin{document}
\begin{alignat*}{4}
\text{This } &\sfrac{\mathcal{O}_{(V',0)}}{\mathcal{O}_{(V,0)}} &\text{ and this } &\sfrac{\mathcal{S}^n}{\equiv_m} &\text{ and this } &\sfrac{A}{B} &&\text{ is \texttt{sfrac}.}\\
\text{This } &\faktor{\mathcal{O}_{(V',0)}}{\mathcal{O}_{(V,0)}} &\text{ and this } &\faktor{\mathcal{S}^n}{\equiv_m} &\text{ and this } &\faktor{A}{B} &&\text{ is \texttt{faktor}.}
\end{alignat*}
\end{document}