Let's say I'm writing a document with 6 chapters. I want to force the table of contents to be split between two pages. The first page would list the first 4 chapters, the second page would list the last 2 chapters.

How can I do that?

If it matters, assume the document class is report.

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Could you explain why you want to do this? –  Seamus Dec 3 '10 at 17:25
@Seamus: Well, the example above is a simplified version. I want to have all chapters listed on the first page, and all appendixes listed on the second. The reason is that currently the ToC is already longer than a single page, so I think it will look nicer if I split it nicely. –  Malabarba Dec 3 '10 at 17:30
@Seamus: It is possible that a pagebreak in the ToC will occur after the first section of a chapter. This is akin to orphans in the main text, and some people may want to avoid it. –  lockstep Dec 3 '10 at 17:33
adding page breaks to a toc is best left for last minute fine tuning, when you know exactly where the "natural" breaks have occurred. it's not at all uncommon. –  barbara beeton Dec 3 '10 at 22:11

Within the body text, right before the fifth chapter, you could add a line break to the `.toc` file, for example:
``````\addtocontents{toc}{\protect\newpage}