Lamedzayin relates the baraita of the four sons to the whole Slifkin debacle and the nature of critical inquiry within Judaism. Required reading.
Hirhurim has a post on the nature of darkness which, of course, related to the biblical plague of darkness.
And you thought my blog was overly specific. Check out: http://pesachotels.blogspot.com/
Hirhurim echoes my thoughts on Mi yimalel, but, of course, says it more eloquently.
This great site has many audio clips of different versions of Ehad mi yodea from around the world.