How much money are you willing to spend? The pfSense hardware range is fairly decent but reaches upwards of $500 USD for the good stuff:
http://store.pfsense.org/SG-4860/
However it looks like with all the SPI features on it only manages about 800Mb/s, though potentially much higher - the 2-core 1.7Ghz version hits 600Mbps so I'd expect the 4-core 2.4Ghz to exceed 1.4Gbps if configured right.