GWAWL (standardized modern form)
Gwawl is given as a daughter of the 4th century northern king Coel Hen. Mention of her survives primarily because she is also said to be the wife (or, less reliably, the mother) of Cunedda Wledig. Since two daughters are attributed to Cunedda, this link might add more names to the list (even though Cunedda's children all have their associations with Wales proper). His children are problematic as a group, however. Each is linked to a major regional place-name in Wales (e.g. Meirion Meirionydd) and, while the names themselves may be valid, the associations with Cunedda may be a political fiction, designed to tie together a wide variety of local traditions. One of the supposed daughters, Tegeingl, is demonstrably fictitious, as the region allegedly named for her can be traced instead to the Brittonic tribal name Deceangli. This makes the northern connection doubtful enough that I've left them out.
Textual Sources
Wawl - JC MS 20 written late 14th c., copied from ms ca. 1200 (the name occurs in a context calling for lenition, so this can be read as Gwawl)Gwawl verch Goel - Bonedd yr Arwyr (see Bartrum EWGT), 15th c. and later mss
The name Gwawl also occurs as a masculine name in the Mabinogi.
Linguistic Analysis
There is no reason not to interpret her name as identical to the common noun gwawl "light, brightness, radiance, splendor". This would derive it from a Brittonic *uál- (GPC). The 4th century date places this name before the loss of final, inflectional syllables in Brittonic, so in addition to proposing a Latinized written form along the lines of Vala, we can suggest a spoken form along the lines of ['wa-la] (assuming an a-stem noun declension), or in English syllables "WAH-lah".