Phidgets - Phidget Encoders
Phidgets are an easy to use set of building blocks for low cost sensing and control from your PC. Using the Universal Serial Bus (USB) as the basis for all Phidgets, the complexity is managed behind an easy to use and robust Application Programming Interface (API). Applications can be developed quickly in Visual Basic, VBA (Microsoft Access and Excel), LabView, Java, Delphi, C and C++. 

What are people building with Phidgets?
737 Flight Simulator ‌ Grouplab Student Project Gallery

Datasheets
1052 Technical Information / QuickStart (.pdf 75 Kb)
1057 Technical Information / QuickStart (.pdf 114 Kb)
COM API Manual - Windows (.pdf 478 Kb)
C API Manual-Windows/MacOSX/Linux (.pdf 339 Kb)
Action Script API Manual(.pdf 470 Kb)
.Net API Manual (.pdf 579 Kb)
Java Docs(.zip 181 kb)

More information can be found on Phidgets website & fourum