CFCom
For anyone who needs to to a lot of COM / ActiveX "interop" with the .NET Compact Framework, take a gander at CF Com by Odyssey Software, Inc.
Admittedly, I haven't had to do a lot of interfacing with COM in my NETCF apps to date (and when I have I have just fired up eVC++ and created a simple wrapper "flat" DLL (which took a little doing - I'm no Bjarne Stroustrup) and then write a managed wrapper using P/Invoke), but if I had a lot of it to do, or use an ActiveX control, I'd likely use CFCom.
-Nino