Finding a low bottom bracket on a Mountain Frame is kind of a trick. I have a Bridgestone CB-1 "City Bike" that has a lower bottom bracket height, and combined with 175mm cranks feels pretty low. I've got he 2.10 Maxis tire under fenders and could tell I was higher when I sized up from 1.9 slicks. I have a nicer 170mm triple that is going on at some point. I hope they don't make the bike feel any higher.
Now, me being me, the bike has another 25 ponds of stuff tacked on so not a light weight. I don't know any specifics, but I would suggest checking out some of the frames that where marketed as city bikes, like the Specialized City Stomper or the Trek 890.
