Some programs/softwares register shell extensions for the benefit of users. But most of the times, this turns out to be an annoyance. Djlizard has put up a wiki which lists the dll files of some softwares like Nero Media Scout or Microsoft Office Language Bar, etc which you can unregister.

To unregister a DLL, click on Start, then Run…, then type: regsvr32 /u [path-to-DLL] and press enter or click OK. If the path to the DLL contains spaces, enclose the entire path in quotation marks. To re-register the DLL, use the same command but without the /u flag.

Ahead Nero 7.x
DLL name/path- “%commonprogramfiles%\Ahead\Lib\MediaLibraryNSE.dll”
Function- “Nero Scout” in My Computer

Corel Paint Shop Pro X
DLL name/path- “%commonprogramfiles%\Corel\PSPThumbShellExt\PSPThumbShellExt.dll”
Function- Explorer.exe .psp/.pspfile thumbnail capability

Grisoft AVG
DLL name/path- avgse.dll
Function- Context menu extension

Intel Graphics Accelerator drivers
DLL name/path- igfxpph.dll
Function- Desktop context menu

Microsoft Office
DLL name/path- msimtf.dll
DLL name/path- msctf.dll
Function- Alternative User Input Text Input, ctfmon, Language Bar

Microsoft Windows XP
DLL name/path- cabview.dll
Function- Internal cab file functionality

Microsoft Windows XP
DLL name/path- shimgvw.dll
Function- Explorer.exe image thumbnails, Windows Picture and Fax viewer, and many more (unregistration not recommended)

Microsoft Windows XP
DLL name/path- shmedia.dll
Function- Explorer.exe video thumbnails

Microsoft Windows XP
DLL name/path- zipfldr.dll
Function- Internal zip file functionality

Djlizard Wiki