So a friend and I are trying to figure out the following:

Besides her own, name the syndicated talk shows (past & present) that were produced by Oprah Winfrey’s production company, Harpo.

So far, we've come up with four: Dr. Phil, The Dr. Oz Show, Rachael Ray, and The Nate Berkus Show. I'm trying to recall if there was more. I want to say The Gayle King Show from the '90s and The Doctors are also on that list, but I'm not too sure. Are we missing anything?

I am not sure about the following show being syndicated or not,but Harpo also has Harpo Radio.Inc,with many radio talk shows,but again I am not sure if those are syndicated or not,or if you are even interested in those or not,but if you are,I can list them,just let me know. She also has Harpo print,LLC,which is like the other two,but in print form.Then she also has Oprah Winfrey Network [OWN]
with the following shows,but unsure if they are syndicated or not.
The Gayle King Show
Our America with Lisa Ling
In the Bedroom with Dr. Laura Berman
Enough Already! with Peter Walsh
Back to your original question,here are the shows you have not listed,but I am not sure if they are syndicated or not:
The Rosie Show 2011-2012

Super Soul Sunday 2011- present

lyanla:Fix my Life 2012-present

Oprah's Next Chapter 2012-present

Oprah: Where Are They Now? 2011-present

Oprah's Master Class 2011-present

Oprah's Lifeclass 2011-present