General purpose:
- Online Etymology Dictionary
- Google Books, set date range and sort by date
- Google Ngram Viewer
Particularly for computing terms:
- Google Groups for Usenet archives (1981 - present)
- DSpace@MIT for the CSAIL archives (1959 - present)
- IETF's RFC archive (1969 - present)
- PDP-10 software archive (~1967 - ~1990), for old source code
- Tech Model Railroad Club dictionary, TMRC 1st & 2nd editions (1959, 1960)
- The Jargon File and its archive (1981 - 2003)
- MIT's The Tech newspaper archives (1881 - present)
- Bitsavers' Software and PDF Document Archive (misc. dates)