2.5GHz
2.5GHz dual-core Intel Core i5 (Turbo Boost up to 3.1GHz) with 3MB L3 cache
500gigs hard drive
4 gigs ram (up to 16g of 1600mhz)
Thunderbolt digital video output
Native Mini DisplayPort output
DVI output using Mini DisplayPort to DVI Adapter (sold separately)
VGA output using Mini DisplayPort to VGA Adapter (sold separately)
Dual-link DVI output using Mini DisplayPort to Dual-Link DVI Adapter (sold separately)
Thunderbolt port (up to 10 Gbps)
FireWire 800 port (up to 800 Mbps)
Four USB 3 ports (up to 5 Gbps)
HDMI port
SDXC card slot
Gigabit Ethernet port
Audio in/out
IR receiver

2.3GHz
2.3GHz quad-core Intel Core i7 (Turbo Boost up to 3.3GHz) with 6MB L3 cache
Configurable to 2.6GHz quad-core Intel Core i7 (Turbo Boost up to 3.6GHz).
1tb hard drive

there are four different cpu configurations so I won't go into as much detail.

2.5ghz quad core i5 up to 3.2 ghz quad core i5. i7 3.1ghz and 3.4ghz is BTO
8gig standard for RAM, upgrade able to 32gigs.

Apple is "introducing" the fusion drive, something PCs have had for a while but only now is coming with macs out of the box. It's basically a SSD and HDD in one. Standard is 1TB but can get BTO of 3 TB.

SDXC card slot
Four USB 3 ports
Two Thunderbolt ports
Mini DisplayPort output with support for DVI, VGA, and dual-link DVI (adapters sold separately)
10/100/1000BASE-T Gigabit Ethernet (RJ-45 connector)