The Repconn headquarters have a very hard door and Bison Steve's has a floor save that's hard. I've encountered others but those are the only two I can think of off the top of my head.
The Underground bunkers in the hidden valley. 1 is free to open, 1 take 25% skill to open, another 50% skill to open, 1 at 75% skill and the last and best one takes 100% lock pick skill. Go have fun.
There is a nice little cache room with some goodies and a sniper rifle behind a hard locked door just East of the strip out past the medical clinic, It is in the first floor of a bombed out house (unmarked).
The Gobi is the only thing I can think of that needs 100 lockpick with no other way around. Entirely replaceable with a fully moded sniper rifle at any rate.