Although I've written a number of art songs, I'm only gradually consolidating them here and making them available. My standard for art song is that if you can't understand 80%+ of the words on first hearing without a printed text, then the project is a failure. So, I think it's really a difficult form. The problem is not just the setting of the text by the composer. Some of the rest of the problem is the poetry itself. Poetry is often written to look at the whole page at once and to be able to go up and down, back and forth, to let it sink in. IMO, that kind of poetry makes for miserable art song. Anyway, lemme back off the soapbox and let you decide for yourself about these...
All of the songs listed, except the "Three Petrarch Sonnets" (Baritone) are available in High, Medium, and Low.
If you are looking for "Arrangements and Derangements of Schubert," that is over at EC Schirmer. That includes this gem, "DIE Forelle!"
If you are looking for songs from "Essentials." You can get that directly from EC Schirmer.
Those six songs have lyrics by Reg Huston. including "When time no longer has trust in me," "Heaven's Gaze," and "Person in the Moon."