Cynan (CUN an) was a legendary 9th-century warrior, and there were also a couple of early kings with the name. It means 'little dog' (from ci, Welsh for dog + nan diminutive)
Meilyr (MAY leer) - various sources I've seen say it's from Brythonic and means 'great king' - can't personally verify that. I love it.
Llyr (lleer) - another old one that pops up in folk tales and early genealogies. It may once have been the name of a deity, the same as the Irish sea god
Lir, but again, not verifiable. There are quite a few around where I live.
I pronounce
Aneirin &
Aneurin the same - an AY rin, ay to rhyme with
May. I really like it too.