The EPU chips

We've seen Asus' Stack Cool 2 on older mainboards, and the Stack Cool 2 on the P5Q comes with heatsink on the bottom of the board dedicated to the MOSFETs.

Silicon Image SIL5723 supplying 2 SATA 3.0Gbps ports. RAID 1 can be enabled automatically without configuration via a simple software. Touted as Asus' Drive Xpert, it can automatically back up your files.

Marvell 88SE6121 Storage controller supplying the IDE and eSATA port

Analog Devices AD2000BX 8 Channel High Definition Codec.

A summary between the differences on the 3 boards before I continue!