This is the big one, Rogers' therapy raison d'etre. Person-Centered Therapy advocated for Unconditional Positive Regard, use of a reflective technique, and a more egalitarian counseling relationship between counselor and client. Here's Rogers talking about Person-Centered Therapy: https://www.youtube.com/watch?v=DjTpEL8acfo
2. Unconditional Positive Regard
This is the concept that we should have Unconditional Positive Regard for clients, even if our world views are drastically different than theirs, and even if we find their behavior morally repugnant. It's a real growing experience when you have been taught to have Unconditional Positive Regard for all people.
3. Egalitarian counseling relationships
In previous counseling theories, the therapist was automatically in a "one-up" position in the therapeutic relationship. Think of a see-saw where the therapist is higher up than the client. There's an inherent "expert" in the counseling relationship. Rogers promoted a more egalitarian, or equal, relationship between counselor and client. Now the counselor and client on the see-saw could look at each other directly. Rogers was also one of the first therapists to use the term "client" rather than "patient".
4. Reflection as a therapeutic technique
It's amazing how just saying "So you're feeling really angry" can be a powerful therapeutic tool.
5. One-third of the "Gloria" treatment team
Watch Rogers in action, then watch Fritz Perls (Gestalt) and Albert Ellis (REBT).
Here's Rogers talking with Gloria:
There's something so warm about Rogers' technique. Gloria later corresponded with Rogers and his family until her death at the age of 50.
6. A counseling theory to train on
When I did my training at the University of Florida, we first learned, then used, Person-Centered Therapy techniques. It's such a pure form of therapy - the techniques are the fundamentals you need to learn before you delve into other theories and therapeutic techniques.
Rogers' 19 propositions of Person-Centered Therapy, along with Rogers' bio, can be found here: http://en.wikipedia.org/wiki/Carl_Rogers
I'll add here that by no means am I a Person-Centered Therapy expert, nor am I an expert on Rogers. I know some of you are. I have Unconditional Positive Regard for you. :)