WPF 1. WPF ComboBoxEx:
blog.catenalogic.com

2. GOOGLE
2.1. wpf binding default value
2.2. wpf FallbackValue combobox
2.3. wpf combobox default (null) value

WPF triggers
drwpf.com

WPF binding debug jimmangaly.blogspot.com

WPF binding
bea.stollnitz.com

WPF Wpf listbox button in datatemplate