What is a USB transceiver?
A USB transceiver is usually a chip that implements the hardware parts of the USB protocol for a end device.  Nowadays dedicated chips for this are not used much because USB peripherals are built into microcontrollers.  The tighter coupling between the firmware and the USB peripheral allows for higher speed, easier interactions, no need for a external bus like SPI, and of course it all comes on a single chip.  Take a look at the Microchip PIC 18F2550 as a example.

Some newer and larger micros have USB host or OTG (stripped down host) capability.  A USB host is a lot more complicated than a USB device, so you generally will find this in micros with larger RAM and program memory, like some of the PIC 32 from Microchip for example.