I was actually eyeing off a few pre-1990 domains, including sesqui.net, earlier this evening -- I generally use the service "ExpiredDomains.net" for searching and sorting by "Whois Birth Year" to find the old ones. Despite it's name, it's actually incredibly useful just to search across various domain marketplaces regardless of if they're expiring or not.

(Un)fortunately most of the super cool ones are way outside of what I budget for my "cool things to have (that don't take up any physical space)" spend.