I have grouped sections nicely below of chapters in ToC, so that there is no space between chapter and following sections, but there is some space between last section and following chapter. All this is done using memoir:

\setlength{\cftbeforesectionskip}{4pt}
\setlength{\cftbeforechapterskip}{16pt}


The problem is that chapter-like entries in the frontmatter (e.g. Foreword, Abstract) will have relatively large vertical space in between. What I would like to have is grouped´ frontmatter chapter-like entries with 4pt vertical space, and 16pt space between last entry of the group (say, ToC or LoF) and the first chapter. Something like this:

Foreword
Abstract
List of Figures

Chapter 1 Introduction
1.1 Section title
1.2 Section title

Chapter 2 Theory
2.1 Section title
2.2 Section title

Bibliography

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Here's one possible solution using the etoolbox package to patch the \chapter command to add some spacing to the ToC; the change is at the point the spacing is required:

\documentclass{memoir}
\usepackage{etoolbox}

\setlength{\cftbeforesectionskip}{4pt}

\begin{document}

\tableofcontents

\chapter*{Foreword}
\chapter*{Abstract}

\chapter{Chapter One}
\section{Section One One}
\section{Section One Two}
\section{Section One Three}
\section{Section One Four}

\chapter{Chapter Two}
\section{Section Two One}
\section{Section Two Two}
\section{Section Two Three}

\chapter{Chapter Three}
\section{Section Three One}
\section{Section Three Two}
\section{Section Three Three}
\section{Section Three Four}
\section{Section Three Five}

\end{document}


The resulting ToC:

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Thank you for the quick answer, it worked perfectly! Maybe this needs new Question, but: I use small caps for the chapter entries, and the grouped entries look ugly´. Is there a way to change them to non-small-caps? –  TKO Nov 19 '12 at 15:34
@TKO as you said, this deserves a new question; please include in your new question a complete sample document (as the one in my answer) showing the relevant settings and illustrating the problem mentioned. –  Gonzalo Medina Nov 19 '12 at 15:42
Done! Entry is in tex.stackexchange.com/questions/83377/… Thanks again! –  TKO Nov 19 '12 at 17:27

Gonzalo Medina answer is very good for automated behaviour. If you need only to act once or twice for specific cases, you should add manually the space. This is to be used with care, since the general equilibrium of the toc can be altered dramatically.

This is done with

\addtocontents{toc}{\vspace{xpt}}


with x being a positive or negative value, written just before your chapter, section, part etc. entry in the text.

You can also use the \addvspace command, but only for positive values.

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