Probably "Your Time Is Gonna Come/Black Mountain Side" off 'Led Zeppelin', if only because I can't get the complete studio recording of "Black Mountain Side" any other way.
This could be a moot thread if you have a functioning and recordable turntable, can do a 'slip cue', and a recording device (tape or CD) or mixer. Most satisfying and most fun if you have 2 turntables and do the slip cue live.
Then you can make your own interactive segues.
I suppose any recording where one song follows another would qualify as a segue, on any extant album. And could include any recordings you make for your own use.
Any medley would automatically count as a segue too. I do a few medleys, mostly full song, where the last note of the initial song is also the first note of the following song. For example, my last ritardando note of "Spanish Harlem" (as instrumental or with vocal) doubles as the first note of "Maria Elena" done as an instrumental. Easiest to do when the key is the same. I also do the intro, verse, and bridge from "Roundabout" as an intro to "Pipeline", all instrumentally on 12 string. Or "Ghost Riders in the Sky" where instrumental + vocal elides into slapped chord rhythm to start "Apache", from the Jorgen Ingmann instrumental version. You get the idea.
Don