You can get an effect like the shading on the go stones in the picture with radial shading. I don't know how to get radial shading off-center, so some clipping is needed:
\begin{tikzpicture}
\begin{scope}
\fill[black] (0,0) circle (0.5);
\clip (0,0) circle (0.5);
\shade[outer color=black, inner color=black!30] (-0.15,0.5) circle (0.7);
\end{scope}
\end{tikzpicture}

(source: caramdir.at)
The scope is needed in order to have the clipping only applied to the shading.
I had some time to kill and the following is the result:

This is produced with the following code
\usetikzlibrary{calc,shadows}
\newenvironment{goboard}{%
\begin{tikzpicture}[
scale=0.5,
stone/.style={drop shadow={shadow xshift=0.03, shadow yshift=-0.05}},
black-stone/.style={black!80},
black-highlight/.style={outer color=black!80, inner color=black!30},
black-number/.style={white},
white-stone/.style={white!70!black},
white-highlight/.style={outer color=white!70!black, inner color=white},
white-number/.style={black}]
\fill[brown!80] (-1,-1) rectangle (19,19);
\draw[black] (0,0) grid (18,18);
\draw[thick,black] (0,0) rectangle (18,18);
\fill (3,3) circle (0.1);
\fill (3,9) circle (0.1);
\fill (3,15) circle (0.1);
\fill (9,3) circle (0.1);
\fill (9,9) circle (0.1);
\fill (9,15) circle (0.1);
\fill (15,3) circle (0.1);
\fill (15,9) circle (0.1);
\fill (15,15) circle (0.1);
}{%
\end{tikzpicture}
}
\newcommand\gostone[4][]{%
\begin{scope}
\fill[stone,#2-stone] (#3,#4) circle (0.45);
\clip (#3,#4) circle (0.45);
\shade[#2-highlight] (-0.15+#3,0.5+#4) circle (0.7);
\end{scope}
\node[#2-number] at (#3,#4) {\sffamily\bfseries{#1}};
}
\begin{goboard}
\gostone[4]{black}{2}{2}
\gostone{black}{3}{3}
\gostone[2]{black}{2}{5}
\gostone[3]{white}{3}{1}
\gostone[1]{white}{5}{2}
\gostone[5]{white}{8}{2}
\end{goboard}
The syntax for the goboard environment and \gostone command is modeled after the psgo package.