This is killing me. I think I remember, either a kid on a project I worked with once was telling me about it, or I watched an EEV blog and he mentioned it like off hand. It was a high level USB analyzer with a BNC connection and a low level port so you could connect a logic analyzer and/or a scope and it would tell you the high level USB status. 

I know I'm never going to find it, but I was very reasonably priced IIRC