Add: 2 + 2 = {{ 2|add:2 }}

Capfirst: {{ "capitalized"|capfirst }}

Centered:
<pre>
{{ "center"|center:20 }}
</pre>

Date format:  {{ date_var1|date:"r" }}
DateTime format: {{ datetime_var1|date:"r" }}

Escape JS: {{ "\" '"|escapejs }}

First letter: {{ "first"|first }}

Fix ampersands: {{ "&"|fix_ampersands }}

Force_escape: {{ "<b></b>"|force_escape }}

Joined: {{ list|join:", " }}

Last: {{ "last"|last }}

Length: {{ list|length }}

Length is 2?: {{ list|length_is:2 }}

Left adjust: 
<pre>
{{ "left"|ljust:20 }}
</pre>

Line breaks: {{ "Line 1\nLine 2\nLine 3"|linebreaksbr }}

Lowercase: {{ "LOWERCASE"|lower }}

Right adjust:
<pre>
{{ "right"|rjust:20 }}
</pre>

Uppercase: {{ "uppercase"|upper }}

URL Encode: {{ "Let's go!"|urlencode }}