Well, Mick, it's a lurvely one and is in vol 3 (if you have the 6 volume version) of Joseph Parry's Cambrian Minstrelsie. I came across it being sung by a Patagonian Quartet (something like Pedwar y Peithiau) and thought it drop dead gorgeous.

As you of all people will see, it's the same metre as Ar Hyd y Nos / All Through the Night and can be sung on that tune if you fancy a major key. (the CM version is in the minor - oh, so nice).

Another tune which I've only recently come across, again in the major, is Gwylan y Mor in "Old Welsh Airs". That works and is also a) unfamiliar to people and b) very lyrical.

regards
siân