Mickey MacConnell (Ireland): singer/songwriter ----- a true wordsmith, who puts his heart and soul into his music.
Chris Terry (Cornwall, UK): a wonderful singer.
Mike O'Connor (Cornwall,UK): a singer /songwriter /instrumentalist /musicologist /storyteller /researcher/publisher, who is a joy to listen to and both as a performer and as an educationalist.
Iain Ap Sion (Wales): a fine singer/musician within the Welsh tradition.
Gilles Servat (Brittany): singer /songwriter /writer /storyteller.
Claire Kilgallon (Isle of Man): a fine singer of traditional Manx songs.
The above are all people I know and enjoy hearing.

From recordings and concerts : Mary Black, Rita Connolly, Maura O'Connell, Luke Kelly, Johnny McEvoy, Iarla Ó Lionáird, Triona Ní Dhomhnaill, Liam Clancy and Tommy Makem (All from Ireland)

Andy M Stewart, Cairistiona Primrose and Flora MacNeil (Scotland)
Joan Baez,(USA)
Kate & Anna McGarrigle, Stan Rogers & Garnet Rogers (Canada)
Márta Sebestyén (Hungary)

Groups : I Muvrini & Barbara Furtuna (Corsica), Battlefield Band and Capercaillie (Scotland), Altan, De Dannan, Chieftains, & The Dubliners (Ireland), King Chiaullee & Mactullagh Vannin (Isle of Man), Avel Dro (Brittany), Coreopolis (Italy), Kimber's Men and Hanging Johnny and Show Of Hands (England)

I also enjoy Greek, Bulgarian, Hungarian & Romanian singimg and traditional music.

Just a small sample list of the folk singers and folk groups I enjoy hearing and no disrespect to any individual or group not listed here.
I've taken note of the previous posts and will have a look for the many artists mentioned that I've not heard of until now. The Mudcat is a great educational resource. It's been very interesting to see other people's favourites lists. Thanks to all for posting, mudcatters !