WinSparkle is a heavily (to the point of being its almost-port) inspired by the Sparkle framework by Andy Matuschak that became the de facto standard for software update on Mac OS X. It shares its aesthetics and goals:
The library is easy to use and distribute. WinSparkle.dll doesn't have any additional dependencies (not even dynamic CRT), all you have to include with your app is this file. And its API is in C and can be used from any language.
WinSparkle's UI uses native Windows controls and looks well in any application. And it runs in a separate thread, so you don't have to worry about compatibility with your GUI toolkit of choice (be it wxWidgets, Qt, WinForms, WPF, ...).
WinSparkle is still under development and doesn't (yet!) have all Sparkle's features. See what features are planned.