My favorites are:
Free: Coolors.co (Web App) - Great app, really easy to use (you just hit spacebar to generate a new palette) you can match up to 5 colors in harmony and manipulate them however you like, with some interesting features like locking one color and getting the others to match it (and matching the locked one settings too). If you want to create an account, you can save all your palettes, or do some screen caps also does the job : )
Paid: Aseprite's RGB and RYB color wheels - Just amazing, does everything an awesome color harmony wheel should do, with the most common presets available like complementary, triads, etc, you can also create and load presets.
