RGMII,SGMII,XAUI

MII   - Media Independent Interface - 100 Mbps
GMII  - Gigabit MII - 1 Gbps (24 pins) (8TX - 8RX)
RGMII - Reduced GMII - 1 Gbps (12 pins) (4TX - 4RX)
SGMII - Serial GMII - 1 Gbps (8 pins) (2TX - 2RX)
XAUI  - XGMII Extender - 10 Gbps (XY pins) (8TX - 8RX)
SPI-4.2 - System Packet Interface Level 4, Phase 2 (16TX - 16RX)

The Media Independent Interface (MII) is a standard interface used to connect a Fast Ethernet (i.e. 100Mb/s) MAC-block to a PHY. The MII may connect to an external transceiver device via a pluggable connector or simply connect two chips on the same printed circuit board. Being media independent means that any of several different types of PHY devices can be used without redesigning or replacing the MAC hardware.

Gigabit Media Independent Interface (GMII) is an interface between the Media Access Control (MAC) device and the physical layer (PHY). The interface defines speeds up to 1000 Mbit/s, implemented using an eight bit data interface clocked at 125 MHz, and is backwards compatible with the Media Independent Interface (MII) specification.

Reduced Gigabit Media Independent Interface (RGMII) specifies a particular interface between an Ethernet MAC and PHY. RGMII uses half the number of pins as used in the GMII interface. This reduction is achieved by clocking data on both the rising and falling edges of the clock, and by eliminating non-essential signals (carrier-sense and collision-indication). Thus RGMII consists only of: RXC, RD[3:0], RX_CTL, TXC, TXD[3:0], and TX_CTL (12 pins, as opposed to GMII's 24).

The Serial Gigabit Media Independent Interface (SGMII) is a sequel of MII, a standard interface used to connect an Ethernet MAC-block to a PHY. It differs from GMII by its low-power and low pin count serial interface (commonly referred to as a SerDes).

XAUI is a standard for extending the XGMII (10 Gigabit Media Independent Interface) between the MAC and PHY layer of 10 Gigabit Ethernet (10GbE). XAUI is pronounced "zowie", a concatenation of the Roman numeral X, meaning ten, and the initials of "Attachment Unit Interface".

Reference:
http://uiway.blogspot.sg/2009/03/rgmiisgmiixaui.html
http://www.altera.com/technology/high_speed/protocols/spi_42/pro-spi_4.2.html