There’s Kdenlive and OpenShot that are maybe the most well-established, but they we’re both very buggy the last time I dealt with them, and they’re nowhere near featureful as what’s available commercially.
I think we could benefit from a well-know MovieMaker equivalent. Something that isn’t featureful, but is reliable (read: doesn’t crash) and intuitive.
Yes, there are a lot of players, especially on the Windows side in the under $100 price range, but nothing I've used has been comparable to iMovie on the Mac. It's the one void that hasn't been filled for me since switching from Mac to Windows.
I've purchased Cyberlink PowerDirector, Corel VideoStudio and Premiere Elements, and I didn't find them to be very good. There's too much of a sloppy "kitchen sink" mentality to them.
I actually found Windows Movie Maker to be better than the aforementioned products, but that got discontinued without a replacement for quite some time. There's now a "Video Editor" application which is part of "Photos" that is serviceable, but I would gladly pay a Windows app that is akin to iMovie - simple, focused and functional.
Edit: Not Open Source though, woops. Still a good sibstitute since Microsoft doesn't host Movie Maker anymore.
Once I can create the flashy animation style stuff I regularly create and not just Windows XP Movie Maker-level animations, I'd pay any price and switch to Linux in a heartbeat.