Any Olympia meetings but nearly every sort of meeting that is open to the public will include some sort of public comment session.  Typically you get about 3 minutes or so.

This is all I could find about the committees and public testimony. 

http://www.ci.olympia.wa.us/citygovernment/advisory/Roles_Expectations.htm

 "Advisory Committee activities may include study of critical issues, hearing public testimony, independent research, and reviewing staff reports and recommendations – all of which is intended so that the committee is prepared to discuss, formulate, and forward well-developed, thoughtful recommendations to the City Council in a timely manner."

"Safety is a tyrant's tool; no one can be against safety."--Unknown

I can't speak for the Planning Commission, but there's usually an opportunity at the beginning of all advisory committee meetings for public comment. It depends on the committee how they handle it though. The city council has been working on standardizing all the various advisory committees so that they are all consistent to a certain degree.

I'm one of the co-chairs of the Bicycle and Pedestrian Advisory Committee, and we traditionally have had a public comment time at the beginning of each meeting, and we usually invite anyone who shows up to stay for the rest of the meeting.

FYI, there are three vacancies on the Planning Commission (and 3 on BPAC), among others. The deadline for applications is next Monday, February 25th. If anyone is interested in applying there is more info here.