We have some very good conferences, although a lot of the more popular ones are fairly dependent upon having attendings who are good teachers/willing to put in some extra time.
I'm not sure what you mean by a "CPC" conference...
For AP we have two types of "unknowns" - once a month we have a more formal conference that all of the attendings and residents attend. The attendings take turns selecting cases for this conference, which we usually get 1-2 weeks prior. During the session we have to show the slides ourselves, describe the features, give a differential and also discuss what additional studies/stains we would want and be prepared for additional pimping.
Many attendings will also give us "unknown" slides to review a day or two prior if they will be using them for a multi-headed scope-based lecture. Those are usually easier to prepare for because we all know what the topic/organ system is and the pimping during lecture is usually pretty benign (and PGY appropriate).
We have CP "unknowns" twice a month - one session is hemepath and the other alternates between the other fields (chemistry, molecular, blood bank, micro, etc.). These are usually pretty useful, depending upon what the attending running the conference decides to do. Hemepath staff usually give us slides of PB, BM, LN or body fluids. The other attendings usually give us some sort of practice questions/cases which they may or may not hand out ahead of time. A lot of the residents particularly like it when the blood bank director uses questions to make a Jeopardy game.
Once a month our program director does a board review conference which is excellent. It is run like a mini-test and she usually shows images (gross, micro, EM, etc.) and the questions are a mix of primary "what is the diagnosis" and secondary/tertiary-type questions. We then immediately go over the answers during the second half of the conference. She'll occasionally make up a slide-based quiz too.
Another conference that we don't have very often, but people really like, is an attendings vs. residents Jeopardy game (called the "Gross Bowl") that the chief resident(s) make up once or twice a year.
I'm not sure about other topics, but I would NOT recommend the CAP lab admin/management online webinars/VMCs. We did those my first year and the vast majority (all except for one or two) sucked. They were a complete waste of time and were often not geared towards residents/M.D.s and/or the speaker was mind-numbingly boring. Our head of CP decided to start doing a lab admin curriculum with us instead, which is much better.