For a freebie suite of controls, I was impressed.  The toolkit includes all your basic controls (Label, ComboBox, etc), 38 in all, and are very customizable.  You can also apply out of the box themes, such as Office2007, also free.  It integrates seemlessly into Visual Studio (I was using VS2005) and includes a very nice demo app that shows off what all the controls can do.

Also in the Krypton family are the Ribbon, tab control, and workspace control.  These are upgrades that you have to pay for, but still cheap when you consider all the very expensive alternatives out there.

Next time you are building an little app from the ground up, consider using these controls.  You should be able to make your app look a ton better at no extra cost.