As for lowest BF%, Jerry Rice is always in the running. In fact, once a doctor told him that if he didnt put on some fat, he'd die (his BF% was rumored to be between .8-3.0% at the time). That sounds crazy if you ask me. I do know that he trains like crazy though.
Tony Mandarich was big in his day, but isn't that impressive by today's standards. He was "only" 6'6'' 315 or so. There are guys now 6'8'' 350+.
I'll have to go with John Randle. The man carries 290 lbs on a 6'2'' frame without any fat.
Another dude whose guns impressed the fuck out me was Amos Zerowue (sp?). We played West Virginia one year, and his arms were the biggest on the field, including both teams linemen. He ran for 234 yards, so i guess his legs work pretty well too.