Couldn't tell you when most of my last flights were, but I can approximate some of them. I'm sure I'm forgetting a model or two.

Vickers Vanguard, LHR-GLA, May 1972.
727-100. Who knows when? I was on the last of UA's first 727-100, SFO-SEA, in 1992 (give or take a year). Met my brother at SEA, and he then took the employee-only flight SEA-BFI.
737-200. Who knows when?
707-320, HK (SPIA - South Pacific Island Airways), HNL-GUM, 1 Oct 1984.
727-200. Who knows when?
DC9-30. Either OMA-STL or STL-OMA, 1982 or 1983 (one direction was EA DC9-30, the other was TW 727-200, but don't remember which was which way).
CV-580, RC, MKE-ORD, summer 1980.
L-1011. DL, ATL-PDX, I think about 1993.
A-310. DL, CLE-MCO, 1992.
DC-6. RNO-SFO, 1 week before UA retired them (1968?).
747-200. ORD-SFO, early 1990s. Was supposed to be a DC-10 (wanted a last flight before they retired) but suffered a plane swap (in this case, "suffered" is definitely the right word for that flight).
720. Either SFO-ORD or ORD-SFO, who knows when?
EMB-120: SEA-EUG, Thanksgiving 1986.
DC-8-30/50. Who knows when? On UA.
DC-8-6x/7x. Later than the other, but again, who knows when?
737-300. Who knows when?
737-400. US, CLT-ORD, but don't remember which trip it was.
737-500. Who knows when?