I'll do my best to try to correlate what I see are similarities between some hardcore bands and metal bands. (as an aside, I really liked Neurosis' "Pain of Mind", very under-appreciated hardcore album)
Agnostic Front definitely had an influence (Napalm Death covered them)
Cro-Mags (could be counted as thrash, depends on how one views it)
Infest and Siege (proto-grind)
Black Flag, who practically turned metal with their later material.
Void, a short lived hardcore band whose guitarist's riffing style is an interesting one for their time period, as his riffing calls to mind thrash and even a bit of death metal.
Swedish first wave hardcore bands, like Totalitar and Anti-Cimex, definitely in my view had a hand in helping out the soon-to-be-flowering death metal scene in their country.
Other bands that may be less significant to metal's development, but are still worthy of praise, are Minor Threat, Bad Brains, Circle Jerks (first 2 albums), Descendants, Die Kreuzen, and Fear.