Question

Well obviously Ruby and Sass, but what are some other ones?

Answer 1

Wiki has a list

http://en.wikipedia.org/wiki/Mixin#Programming_languages_that_use_mixins

To quote:

Programming languages that use mixins

Other than Flavors and CLOS (a part of
Common Lisp), some languages that use
mixins are:

* ColdFusion (Class based using includes and Object based 
  by assigning methods from one object to another at runtime)
* Curl(with Curl RTE)
* D (called "template mixins")
* Factor[citation needed]
* Fantom
* Ioke
* JavaFX Script
* JavaScript
* Object REXX
* OpenLaszlo
* Perl[3]
* PLT Scheme (mixins documentation)
* Python
* Ruby
* Scala
* Smalltalk
* Strongtalk
* Vala
* Visual Dataflex
* XOTcl/TclOO (object systems for Tcl)[4]

Some languages like ECMAScript
(commonly referred to as JavaScript)
do not support mixins on the language
level, but can easily mimic them by
copying methods from one object to
another at runtime, thereby
“borrowing” the mixin’s methods. Note
that this is not possible with
statically typed languages, where an
object’s signature is fixed at compile
time.