Here is a list of Elvish names and phrases from The Art of The Lord of the Rings by J.R.R. Tolkien that I think might be previously unpublished. Some or all of these have already been mentioned online, but I do not know if all of them have been listed in one place on an English-language forum. Transcriptions are from Hammond and Scull unless noted otherwise.

I have only read the book in translation, so if the picture numbers do not match the original or something else seems wrong, that could be the reason.

1. Tarn na Donnrhyn

Figure 12. A place name south of the Shire; below it is written "Burntshrub Moors" (reading uncertain).

2. KOLMA[N]OH[TA] (in the Latin script)
kolmanohta, ikolmanohta (in Tengwar)
I·TARKOLMA·HERU (in the Latin script)
itarklmaheru, itarkolmaheru (in Tengwar)

Figure 45. All transcriptions are mine. Hammond and Scull's translations are roughly 'war of the Ring' and 'the lord of the Ruling Ring' (my back-translations).

3. Caernost

Figure 104. This earlier name of Calembel has been published, but Christopher Tolkien reads it as Caerost (The War of the Ring p. 437). I cannot see the n myself.

4. (sea of) Rûnaer

Figure 157. Earlier name of the Sea of Rhûn.

5. Haeren

Figure 160. A place name in western Gondor.

6. Sínome Maruvar Tenn' Ambarmetta'

Figure 181. A variant of the "Sinome maruvan..." phrase. I do not know if this or the next one have been published elsewhere.

7. Sínome mar[u] far ar h[i]ld[i]ny[a] tenn'amb[a]rmetta (in Tengwar)

Figure 182. Another variant.

8. fe[a]nóre[a]
i tengwar feanórie
(In Tengwar, my transcriptions. In fe[a]nóre[a] the tehta for a has been omitted.)

There are also words in Tengwar I cannot transcribe with any confidence:
?ll?me
rai sarna
ombórea

Figure 189. On a page associated with Appendix E.