Return to the Temple of Elemental Evil is great. I'm not sure about how old-school you'd find it, though, as it's pretty logical. But it starts at 4th level (and takes characters up to 14th), and ...
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... it's got a few minor dungeons and stuff in the early part, but a 245-or-so-rooms ring-shaped mega-dungeon follows. It's peopled with competing evil splinter cells of an evil sect alternating with monsters and ... well, more cutlists and more monsters. And from there, on to the grand finale in the hub inside that ring.
As the GM, you can run it pretty dynamically (ie with cultists and monsters moving and reacting to developments around them) - or else you can elect to run it old-school, ie leaving each encounter sitting in its room waiting for the PCs to come kicking in the door. Well, more or less.
If you want the genuine old-school feel, though, (ie discarding logic, ecology, and stuff), Rappan Athuk may be more your cup of tea.