The M7 is the M16 version of the same bayonet design that's been used since WWII.
[img]arms2armor.com/Bayonets/usm7a.jpg[/img]
[img]www.uscav.com/prodInfo/enlarged/22204L.jpg[/img]
Vietnam-era M7
[img]www.rguns.net/knives/knif05.lg.jpg[/img]
Current-issue-style M7
[url]www.eickhorn-solingen.com/englisch/inhalt/products/bayonets/bayonets_1.html[/url]
[url]www.sarcoinc.com/bayo-eick.html[/url]
The M9 is the current bayonet, and has gone through a few minor revisions. They have been made by Buck and Phrobis, with the largest contractor being Lan-Cay, who currently shares the current contract with Ontario.
[img]quarterbore.com/images/m9ontario.jpg[/img]
The M7 is a better bayonet, while the *better* M9s are probably the better field knives. The quality definitely dropped when Lan-Cay won the contract, though.
-Troy