I don't know any in Miami, but Ft. Lauderdale has metal shows in both The Culture Room and The Revolution.
But there are a whole bunch of venues in Miami as well.. No metal bands play in it, but they are there!
The Jackie Gleason Theater, Section 11, The James Knight Center, Lincoln Theater, Gusman Center, Colony Theater.. Plus the huge arenas/stadiums and such..
ooooh, I saw Dream Theater at that Orlando HoB....great show, front row, recorded for HoB's website. Hell, for all I know it might still be on there.
Hey, what about Bicentennial Field?
I saw Metallica there on that weird stadium tour they did in 1994.....I've never seen a show where people could swim ashore and sneak into the show from boats anchored in Biscayne Bay...and don't expect to ever again, either.