I am sure some ppl have their own companion(s)... so, pls talk about them!
Who are they? How do they complement your character? How did they meet (if you have a backstory to this)?
Amarel almost never goes anywhere without her two best friends, http://lovkullen.net/Emma/Vilja.htm and http://tesnexus.com/downloads/file.php?id=17743. They make for a pretty great (and entertaining) team--Vilja is the healer, alchemist and pvssyrbox, and is decent with a bow; Stoker is the mostly silent (possibly because no one can get a word in edgewise when Vilja's around!) tank, charging headlong into melee combat; and Amarel herself switches between sneaky archery and, when needed, melee.
...Yes, I've basically turned Oblivion from a solo adventure into a party RPG.

But they're so entertaining I just can't regret it.
As for animal companions, Amarel has her faithful black horse, Celethelel. (Whose name I borrowed from http://www.uesp.net/wiki/Lore:The_Song_of_Pelinal,_v_3.) Vilja and Stoker have their own horses as well.