I'm unaware of any such Explorer shell "extensions". For example I've not added any proprietary right-click "open-withs" and my preview for any jpg/gif/png graphics is bog standard "as she came".
You wouldn't necessarily be aware of extensions, since they are designed to be transparent. There are thousands of available extensions for Windows, and if any of these are installed and contain bugs, they can crash Explorer. On fresh retail installs of Windows 7, you shouldn't have any potentially buggy extensions installed, but OEM installs may slip in all sorts of things if it's not the standard OEM version of Windows, and many other programs will slide an extension into place during installation, in order to "improve" your experience with Windows.
I have a mix of straight retail Windows 7 installations and hokey HP OEM installations, the latter clogged with metric tons of garbage bloatware upon delivery. Neither has had Explorer crashes, though. I did manage to remove most of the HP garbage, although it's difficult and HP messes up some system parameters, too. I would have still preferred XP, but it's hard to find XP these days for new machines.
Which desktop appearance are you using? Have you tried Windows Classic? It makes fewer demands on video hardware and software and runs faster, in addition to (possibly) being less likely to expose bugs in a video driver or something like that.