WordPress Plugin: Limit-Post
Limit-Plus controls the maximum amount of characters displayed for an entry on the main page. If the set limit is surpassed, a link to a page with the whole content will appear and the text on the entry will be chopped to that amount of characters, otherwise the content will be showed unchanged.









I can’t hit the site at the moment, however; here is a suggestion in case it doesn’t already handle it.
To allow it to truncate at the nearest lesser word, so you don’t get half a word displayed and then inserting an ellipsis (…/…) at the end to suggest that it ‘continues’ onto another page.
Al.