Banjoman, your question IS rather a tall order, given that even 'must haves' depend very much on taste and personal interest. Still, that's no reason to be rude to you! I apologise for our (nameless, as usual) Guest and hope you won't be put off the Mudcat.
Maybe you could give us an idea of the direction of your interests etc. Personally, because that's the direction my interest takes I'd recommend anything from Scotland, Ireland, England or the American continent that is not country and Western or pop and contains intelligent lyrics written in English and done to a tasteful and preferably unobtrusive backing (or none at all) - e.g. Jeannie Robertson, Brian McNeill, Andy Irvine, Tommy Sands, Phil Tanner, Norma Waterson, Tom Paxton or Gordon Bok, to name but a very few. And if you're into Banjo as a backing instrument you might try Iain MacKintosh, The Dubliners, or Pete Seeger, the greatest of them all.