The T4xx and the X2xx lines have been pretty much the go-to for corporate IT over the last decade. Solidly built, upgradable (except for perhaps the bleeding-edge models), and heaps of spare parts around if needed.

X1 Carbon is amazing (not that old!).

I just do not recommend the Yoga models, the specs look great, but they are insanely slow with huge presentation decks or big excel models.