Large table (ca. 30 columns) covering one or several double pages?
I think that the only feasible option is to split the data into 2n parts:
- first part, columns 1-15, rows 1-24,
\newpage - second part, columns 16-30, rows 1-24,
\newpage - third part, columns 1-15, rows 24-48,
\newpage - fourth part, columns 16-30, rows 24-48,
\newpage - ...
Twenty-four rows is just to put some number. If the data and the header row are homogeneous in height, they should align perfectly.
For the caption, it can go on the left page, but I suggest to set it into a \vbox with prescribed height:
\newcommand{\mycaption}[1]{\vbox to 3\baselineskip{
\vfill\captionof{table}{#1}\vfill}}
where 3 is a number bigger than the number of lines in the caption. For the right page you can say
\newcommand{\fakecaption}{\vbox to 3\baselineskip{}}
and insert \fakecaption after the \newpage; \captionof requires the caption package.
The margins can be overridden either with \newgeometry of the geometry package or simply by inserting each "subtable" inside \makebox[\textwidth]{}.
A possible implementation
\documentclass[a4paper,twoside]{book}
\usepackage{caption}
\newlength{\leftcaptionht}
\newsavebox{\tablebox}
\newcommand{\lefttable}[1]{%
\setbox\tablebox=\vbox{\medskip\captionof{table}{#1}}
\setlength{\leftcaptionht}{\ht\tablebox}%
\box\tablebox}
\newenvironment{doubletable}
{\newpage\ifodd\value{page}\null\newpage\fi\centering}{\newpage}
\newenvironment{widetabular}
{\begin{lrbox}{\tablebox}\begin{tabular}}
{\end{tabular}\end{lrbox}\makebox[\textwidth]{\usebox{\tablebox}}}
\newcommand{\righttable}{\newpage\vbox to\leftcaptionht{}}
\begin{document}
text
\begin{doubletable}
\lefttable{This is a caption}
\begin{widetabular}{ll}
a column long enough to go over & a column long enough to arrive over the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
\end{widetabular}
\righttable
\begin{widetabular}{ll}
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
\end{widetabular}
\end{doubletable}
\begin{doubletable}
\lefttable{This is a caption that occupies more than one line and so has to wrap, so that we
can show that the alignment is correct}
\begin{widetabular}{ll}
a column long enough to go over & a column long enough to arrive over the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
\end{widetabular}
\righttable
\begin{widetabular}{ll}
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
a column & a column long enough to arrive near the right margin\\
\end{widetabular}
\end{doubletable}
\end{document}
If you want a caption on the right pages, it's sufficient to define \righttable differently:
\newcommand{\righttable}{\newpage\vbox to\leftcaptionht{\medskip
\noindent(Table \thetable{} (continued)}}
(or something similar).
The suggestion is to add rows to the tables until they fit on the page and then start a new pair.
you can create the table with ConTeXt, it can split tabulars also in the horizontal direction. The created pdf can then be inserted into your document if you need to run it with pdflatex