In 8051 family, you have a very good option from TI i.e. TUSB3210 and also a few from Cygnal (Silabs - www.silabs.com )
In PIC family you have PIC16C745/765 and few others with on-chip USB ( www.microchp.com )
If you just want USB interface, you can use USB->Serial interface chips like FT232 ( https://www.ftdichip.com ) . This is not a real USB interface. The USB port will be used as virtual serial port, but works great for most applications as you can use any uC having on-chip serial port.