Sho' nuff!
You ain't kiddin'
Ain't that the truth!
Damn straight!
You can say that again
Mmm-hmm...
I hear you


Then there's the hilarious movie "Airplane," in which two guys are speaking "jive," with subtitles in standard English. At one point one guys says "sheeeeeeeeeet" and the subtitle says "How true. How true."