Yeah, even a good number of the steel MTBs from the late 80s-mid 90s are still considered pretty lightweight. The only thing that makes my Breezer heavier than as- stock are the Magura hydraulics and the Sun Rhino Lites, otherwise, it's really light. It's the lightest bike I own and I didn't even try to be a weight weenie.
The pre-1997 steel Stumpjumpers are all Tange Prestige and really light (the red painted frames are fast, but the S-Works team maroon frame is the fastest.)
Also look for Novaras (REI house brand), more uncommon Parkpre, early VooDoos, Konas, and Miyatas. The Miyata cross frames are 700c but can take some really big tires.