On the 1/23/88 Tacoma, WA show they played an early original song, which the true title of is unknown. It's referred to as Raunchola. See Earliest Recordings for more info on that one.
During the late-'89 tour in Europe there was a heavy song played a couple of times. I've mentioned it before, it's called Help Me, and it was played in September of 1991 too, but then in another form. Chad Channing has said that he never knew a name for this song, and that Help Me is as good as any. There are no known studio versions of this. The most available version is from 11/22/89, it's also on numerous bootlegs. Here's a clip of it:
Another song I've talked about before, in the Mid - '89 to Late '90 section, is Token Eastern Song. It was played from 9/13/89 to 1/20/90, and was recorded during the studio session in September '89.
I've also talked about In his hands. It's one of my favourite Nirvana songs, and has been heard three times in late '90 - early '91. Read more about it here.
On 9/25/90 Kurt played acoustically solo on the "Boy Meets Girl" show on KAOS Radio, with their studios in Olympia, WA. He came up to the show and talked with host Calvin Johnson about having some new material he wanted to play. Only 1 ½ songs has surfaced. The incomplete is a cut version of Lithium, and the other song is the one-time performance of a song called Opinion. There are probably more rarities on the full show, but this is all that's available now. Opinion was never recorded more, but there were some requests for it on the 10/21/91 acoustic show in Austin, TX. Rob Holmes, and many others with him, believe that that show is incomplete, and that Opinion might have been played there. But, again, one never knows until we have recordings. Here's a sound sample of Opinion:
Other songs mentioned before are Come on Death, Crisco and Talk To Me, in the Mid - '91 to Early '93 section, and You've got no right in the 1994 Sessions section.
There are also some songs that has been rumoured about, but has never been heard. Read about a them in the next appendix - Never heard songs.