WPF is positioned as a successor to WinForms, but given Microsoft's practice of abandoning toolkits (and what I perceive a s"bloat" in WPF), are there any recommended alternatives?
It depends on your favorite programming language, but Qt is a good Gui toolkit for C++. It has impressive features, is free and as platform independent as it gets for GUI toolkits.
I don't think you need to worry about WPF being abandoned. WinForm was around for a long time, and WPF is the replacement.
Bloat? I dunno... Seems like a huge upgrade from WinForms to me. If there's bloat it's always going to be there because underneath everything is the Win32 API. Until that gets rewritten from scratch I don't think anything will be perfect. And since every toolkit targeted at the Windows platform has to deal with that... I'd rather go with WPF and ReSharper...
Another sign Microsoft is serious about WPF is that it's getting used to make Visual Studio 2010. XAML seems to get used by more than just WPF (Workflow Foundation, Communication Foundation).
I've been coding in WinForms for the past 5 years and I was a bit sceptic of WPF too at first. But after reading a few books and trying out my first application in WPF I'm starting to see the beauty of it!
I keep amazing myself at how little "glue" code is needed in a WPF application compared to how I would have done it in WinForms. Here's an example: I had to show a simple histogram. In WinForms I would have written a custom control and handled the rendering myself. In WPF, I did it all from xaml without one line of code! I just bound the data samples to a list box, replaced the listbox's layout template to an horizontal stack panel, and replaced the item template to rectangles which height is bound to the sample values!
MS does not have a practice of abandoning toolkits (WinForms, MFC, ActiveX and Win32 are all still being actively developed) and the "bloat" is actually new capabilities you may not need right now but there's a good chance you'll need in the future.
If you don't want bloat and use only an API that will be impossible for MS to stop supporting you are more then welcome to work with the Win32 API directly.
Adobe AIR is the strong competitor. If you aim to create cross-platform applications with rich user interface, check out this one.