Run D.M.C. - Walk This Way

Band:  Run D.M.C. feat Steven Tyler and Joe Perry of Aerosmith
Genre:  Rap Rock

I won't say these guys started the Nu-Metal trend, especially since this was much more Rap than Rock.  This is a really important song to mention though, cause even though Run D.M.C. used a lot of electric guitar in their beats already, so kinda of a stepping stone song in the process.

DMC did a lot of that already, so including Aerosmith was basically just step two.

Run D.M.C. - Rock Box

So Run D.M.C. was one of the original rap-rock groups.  They are also absolute classics in the early Hip Hop scene too, so there are a lot of ways you might have heard of them.  They've even done a song with Aerosmith before.

Not having been alive during their beginnings and heyday, I can't vouch for some of the Wiki info I looked at, but checking dates it kinda adds up that this was one of those game changing songs.  Much like when Public Enemy played with Anthrax, or when Jimi Hendrix helped change the guitar game for people, Rock Box helped people realize that rock and rap could coexist.

Later in their career they did drift from their rap rock roots, but it's still good music and worth checking out.