Hentai Ouji to Warawanai Neko.: Henneko BBS

Both are a compilation of animated specials that provides a secondary, more humorous perspective on their respective parent story. Both are relatively short in length and should be watched after watching their parent story. Furthermore, Henneko BBS and the Endymion special are both made and released by J.C. Staff, so the artwork and the quality have a lot of matching parallels. 

If you've been following J.C. Staff for a while, you know that they have a tendency to release very short specials (i.e. just a couple of minutes long) that are relatively funny. They may choose to make fun of certain plot elements or other characters within their respective shows. Fortunately, both specials deliver decently and do not disappoint. If you have a few minutes here and there throughout the day, I would suggest watching both.