Infragistics[
^] is another tool that allows skinning of forms and controls.
I've used both Infragistics and DevExpress. They are both powerful; Infragistics is perhaps more flexible if you want to really customize forms' appearance, but I've always found DevExpress sufficient.
DevExpress is easier to use and its help is far better (not perfect by any means, but much better). Mind you, Infragistics' help may have improved in the 3 years or so since I last used it.
Neither tool is free.