I have the 70-200 f4 IS.....Indoors or outdoors it's an awesome portrait lens....on either my rebel xi, or 5d mark2. Indoors you will need an external flash. The portrait images I get with that are second to nothing.
I also use the 50 f1.4, and the 24-70 f2.8 canon is my basic walk around. I use these both for portraits as well......depending on lighting..and situation. Multiple people, small room, no flash..etc.
I am just a hobbyist...when work gives me the chance.