warning DISCLAIMER: Mentioning stuff from my own shop...
I hate not having stuff to build a good idea on the weekend. That was one of the motivations behind this:
http://arduino-direct.com/sunshop/index.php?l=product_detail&p=214
Several Optoisolators in there, and Other Good Stuff. More here: http://arduino-direct.com/sunshop/index.php?l=product_list&c=36
Me and Parts is dangerous. Ask my Wife :*