Roughly ordered easiest to most difficult.

• A few fields are missing from Settings (extra_plugin_paths) and BrowserSettings (standard_font_family,fixed_font_family,serif_font_family,sans_serif_font_family,cursive_font_family,fantasy_font_family,default_encoding,user_style_sheet_location)
• JS alert box handling,see cef.h HandleJSAlert, HandleJSConfirm, HandleJSPrompt
• Expose Post data on Request object.
• Add support for authentication, seeHandleAuthenticationRequest
• Printing support, seeHandlePrintOptions andHandlePrintHeaderFooter
• Context menu, allow uses to override the display of the context menu and its actions.
• Further improvements to CLR object binding, should be able to dynamically bind returned objects enabling chaining of method calls"obj.GetThing().DoStuff()"
• Full AppDomain support
• Mechanism for giving users control over the creation of pop-up windows
• Provide page load progress (will likely require modification to CEF)

Of course Automated Tests and Bug fixes always welcomed. Whilst I should probably just create feature request issues for each of these, I'll wait until someone requests them.