"My goal is to (someday) build myself a USB-device and I'm thus trying to find a uC family..."

Cypress have a USB controller with on-chip 8051 - it's currenly featuring in articles in the UK editions of Elektor magazine.
I believe that Texas have a similar part.

Triscend have an Application Note/Reference Design describing a USB Device using their E5 8051-based part and an FTDI USB Chip.
The FTDI chip (in the form of a module) has been featured in a number of Electronics World (formerly Wireless World) articles recently.
The FTDI site has a load of useful support stuff.

You should also visit www.usb.org, and try a 'Search' here for "USB"