John, the "Joy, Love and Peace" song that you're asking about is The King

Martin has recorded it several times. The Steeleye Span version is the best to my ears.

Martin's best album? That's a difficult one. I'd probably say Shearwater, but I'd doubt that many would agree.

There are a number of compilations which would be a good starting point. If you let me know what you already have, and what you particularly like, I might be able to offer better advice.

(To answer the original question):
Siege of Delhi
Palaces of Gold
Willie's Lady
Sovay

and every other song anyone else mentioned!