"Excerpt" option in Redactor?
You could use the Redactor's pagebreak plugin. Check out the docs.

If activated in your Redactor config, you will have the option to insert page breaks to your content, via a new “Insert Page Break” toolbar button.

Now you can get the first "page" in your template:

{% for entry in craft.entries.section('blog') %}
    &lt;article&gt;
        &lt;h1&gt;&lt;a href="{{ entry.url }}"&gt;{{ entry.title }}&lt;/a&gt;&lt;/h1&gt;

        {{ entry.richTextFieldHandle.getPage(1) }}

        {% if entry.richTextFieldHandle.getTotalPages() &gt; 1 %}
            &lt;a href="{{ entry.url }}"&gt;Continue reading…&lt;/a&gt;
        {% endif %}
    &lt;/article&gt;
{% endfor %}