I'm running the LA marathon. I also had a new letter of recommendation written for me and I mailed those off. Of course, I sent each school a letter saying the letter of rec is coming and what I liked about each of their schools.
I don't know about other schools, but I called USC and UCI and they both said do not send in additional materials after your interview. UCI gives you a rank, and they will not re-review your application after they notify you of being waitlisted.